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nutrition Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient ...
,
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...
, and
chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, fat usually means any
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
of
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...
s, or a mixture of such compounds, most commonly those that occur in living beings or in
food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...
. The term often refers specifically to
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...
s (triple esters of
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
), that are the main components of
vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or f ...
s and of
fatty tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...
in animals; or, even more narrowly, to triglycerides that are solid or semisolid at room temperature, thus excluding oils. The term may also be used more broadly as a synonym of
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...
—any substance of biological relevance, composed of
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
, or
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
, that is insoluble in water but soluble in
non-polar solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s. In this sense, besides the triglycerides, the term would include several other types of compounds like
mono- Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and many other languages, they are used to coin numerous series of words. For example: * unicycle, bicycle, tricycle (1-cycle, 2-cycle, 3-cy ...
and diglycerides,
phospholipid Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
s (such as
lecithin Lecithin (, from the Greek ''lekithos'' "yolk") is a generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues which are amphiphilic – they attract both water and fatty substances (and so a ...
),
sterol Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the go ...
s (such as
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
), waxes (such as
beeswax Beeswax (''cera alba'') is a natural wax produced by honey bees of the genus ''Apis''. The wax is formed into scales by eight wax-producing glands in the abdominal segments of worker bees, which discard it in or at the hive. The hive work ...
), and free fatty acids, which are usually present in human diet in smaller amounts. Fats are one of the three main
macronutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...
groups in human
diet Diet may refer to: Food * Diet (nutrition), the sum of the food consumed by an organism or group * Dieting, the deliberate selection of food to control body weight or nutrient intake ** Diet food, foods that aid in creating a diet for weight loss ...
, along with
carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
s and
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s, and the main components of common food products like
milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modulat ...
,
butter Butter is a dairy product made from the fat and protein components of churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 80% butterfat. It is used at room temperature as a spread, melted as a condim ...
,
tallow Tallow is a rendered form of beef or mutton fat, primarily made up of triglycerides. In industry, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain technical criteria, includ ...
,
lard Lard is a semi-solid white fat product obtained by rendering the fatty tissue of a pig.Lard
entry in the ...
,
salt pork Salt pork is salt-cured pork. It is usually prepared from pork belly, or, more rarely, fatback. Salt pork typically resembles uncut side bacon, but is fattier, being made from the lowest part of the belly, and saltier, as the cure is stronger ...
, and
cooking oil Cooking oil is plant, animal, or synthetic liquid fat used in frying, baking, and other types of cooking. It is also used in food preparation and flavoring not involving heat, such as salad dressings and bread dips, and may be called edible oil ...
s. They are a major and dense source of
food energy Food energy is chemical energy that animals (including humans) derive from their food to sustain their metabolism, including their muscular activity. Most animals derive most of their energy from aerobic respiration, namely combining the carbohy ...
for many animals and play important structural and
metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
functions, in most living beings, including energy storage, waterproofing, and
thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with ...
. The human body can produce the fat it requires from other food ingredients, except for a few
essential fatty acid Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic ac ...
s that must be included in the diet. Dietary fats are also the carriers of some flavor and
aroma An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sens ...
ingredients and
vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrie ...
s that are not water-soluble.


Biological importance

In humans and many animals, fats serve both as energy sources and as stores for energy in excess of what the body needs immediately. Each gram of fat when burned or metabolized releases about 9 food calories (37 kJ = 8.8
kcal The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of o ...
). Fats are also sources of
essential fatty acid Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic ac ...
s, an important dietary requirement.
Vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrie ...
s A, D, E, and K are fat-soluble, meaning they can only be digested, absorbed, and transported in conjunction with fats. Fats play a vital role in maintaining healthy
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...
and
hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fi ...
, insulating body organs against shock, maintaining body temperature, and promoting healthy cell function. Fat also serves as a useful buffer against a host of diseases. When a particular substance, whether chemical or biotic, reaches unsafe levels in the bloodstream, the body can effectively dilute—or at least maintain equilibrium of—the offending substances by storing it in new fat tissue. This helps to protect vital organs, until such time as the offending substances can be metabolized or removed from the body by such means as
excretion Excretion is a process in which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after ...
,
urination Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...
, accidental or intentional
bloodletting Bloodletting (or blood-letting) is the withdrawal of blood from a patient to prevent or cure illness and disease. Bloodletting, whether by a physician or by leeches, was based on an ancient system of medicine in which blood and other bodily f ...
,
sebum A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest nu ...
excretion, and
hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fi ...
growth.


Adipose tissue

In animals,
adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular ...
, or fatty tissue is the body's means of storing metabolic energy over extended periods of time.
Adipocyte Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. I ...
s (fat cells) store fat derived from the diet and from liver
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...
. Under energy stress these cells may degrade their stored fat to supply fatty acids and also glycerol to the circulation. These metabolic activities are regulated by several hormones (e.g.,
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism ...
,
glucagon Glucagon is a peptide hormone, produced by alpha cells of the pancreas. It raises concentration of glucose and fatty acids in the bloodstream, and is considered to be the main catabolic hormone of the body. It is also used as a medication to tre ...
and
epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
). Adipose tissue also secretes the hormone
leptin Leptin (from Greek λεπτός ''leptos'', "thin" or "light" or "small") is a hormone predominantly made by adipose cells and enterocytes in the small intestine that helps to regulate energy balance by inhibiting hunger, which in turn dimi ...
. The location of the tissue determines its metabolic profile:
visceral fat Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...
is located within the abdominal wall (i.e., beneath the wall of abdominal muscle) whereas
subcutaneous fat The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and macro ...
is located beneath the skin (and includes fat that is located in the abdominal area beneath the skin but ''above'' the abdominal muscle wall). Visceral fat was recently discovered to be a significant producer of signaling chemicals (i.e.,
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
s), among which several are involved in inflammatory tissue responses. One of these is resistin which has been linked to obesity,
insulin resistance Insulin resistance (IR) is a pathological condition in which cells fail to respond normally to the hormone insulin. Insulin is a hormone that facilitates the transport of glucose from blood into cells, thereby reducing blood glucose (blood sugar ...
, and (more controversially) Type 2 diabetes.


Production and processing

A variety of chemical and physical techniques are used for the production and processing of fats, both industrially and in cottage or home settings. They include: * Pressing to extract liquid fats from fruits, seeds, or
alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
e, e.g.
olive oil Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: ...
from
olive The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' ' ...
s * Solvent extraction using solvents like
hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relative ...
or
supercritical carbon dioxide Supercritical carbon dioxide (s) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure. Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as ...
* Rendering, the melting of fat in adipose tissue, e.g. to produce tallow, lard,
fish oil Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), precursors of certain eicosanoids that are known to reduce inflammation in the b ...
, and
whale oil Whale oil is oil obtained from the blubber of whales. Whale oil from the bowhead whale was sometimes known as train oil, which comes from the Dutch word ''traan'' (" tear" or "drop"). Sperm oil, a special kind of oil obtained from the head ...
* Churning of milk to produce butter *
Hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
to increase the degree of saturation of the fatty acids * Interesterification, the rearrangement of fatty acids across different triglycerides *
Winterization Winterization is the process of preparing something for winter. Humanitarian aid In emergency or disaster response situations, such as managed by the UNHCR, winterization activities include the distribution of items including blankets, quilts ...
to remove oil components with higher melting points * Clarification of butter


Metabolism

The pancreatic lipase acts at the ester bond, hydrolyzing the bond and "releasing" the fatty acid. In triglyceride form, lipids cannot be absorbed by the
duodenum The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine m ...
. Fatty acids, monoglycerides (one glycerol, one fatty acid), and some diglycerides are absorbed by the duodenum, once the triglycerides have been broken down. In the
intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans an ...
, following the secretion of
lipase Lipase ( ) is a family of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually ...
s and
bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bi ...
, triglycerides are split into monoacylglycerol and free fatty acids in a process called
lipolysis Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and free fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in fat adipocytes. The most important ...
. They are subsequently moved to absorptive
enterocyte Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase i ...
cells lining the intestines. The triglycerides are rebuilt in the enterocytes from their fragments and packaged together with
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
and proteins to form
chylomicron Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small particle''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein particles that consist of triglycerides (8 ...
s. These are excreted from the cells and collected by the lymph system and transported to the large vessels near the heart before being mixed into the blood. Various tissues can capture the chylomicrons, releasing the triglycerides to be used as a source of energy. Liver cells can synthesize and store triglycerides. When the body requires
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...
s as an energy source, the hormone
glucagon Glucagon is a peptide hormone, produced by alpha cells of the pancreas. It raises concentration of glucose and fatty acids in the bloodstream, and is considered to be the main catabolic hormone of the body. It is also used as a medication to tre ...
signals the breakdown of the triglycerides by
hormone-sensitive lipase Hormone-sensitive lipase (, HSL), also previously known as cholesteryl ester hydrolase (CEH), sometimes referred to as triacylglycerol lipase, is an enzyme that, in humans, is encoded by the ''LIPE'' gene, and catalyzes the following reaction: ...
to release free fatty acids. As the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
cannot utilize fatty acids as an energy source (unless converted to a
ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double b ...
), the
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
component of triglycerides can be converted into
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
, via
gluconeogenesis Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from certain non- carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. In verteb ...
by conversion into dihydroxyacetone phosphate and then into
glyceraldehyde 3-phosphate Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is a metabolite that occurs as an intermediate in several central pathways of all organisms.Nelson, D ...
, for brain fuel when it is broken down. Fat cells may also be broken down for that reason if the brain's needs ever outweigh the body's. Triglycerides cannot pass through cell membranes freely. Special enzymes on the walls of blood vessels called
lipoprotein lipase Lipoprotein lipase (LPL) (EC 3.1.1.34, systematic name triacylglycerol acylhydrolase (lipoprotein-dependent)) is a member of the lipase gene family, which includes pancreatic lipase, hepatic lipase, and endothelial lipase. It is a water-solubl ...
s must break down triglycerides into free fatty acids and glycerol. Fatty acids can then be taken up by cells via the fatty acid transporter (FAT). Triglycerides, as major components of
very-low-density lipoprotein Very-low-density lipoprotein (VLDL), density relative to extracellular water, is a type of lipoprotein made by the liver. VLDL is one of the five major groups of lipoproteins (chylomicrons, VLDL, intermediate-density lipoprotein, low-density lipo ...
(VLDL) and
chylomicron Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small particle''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein particles that consist of triglycerides (8 ...
s, play an important role in
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...
as energy sources and transporters of dietary fat. They contain more than twice as much energy (approximately 9kcal/g or 38 kJ/g) as
carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
s (approximately 4kcal/g or 17kJ/g).


Nutritional and health aspects

The most common type of fat, in human diet and most living beings, is a
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...
, an ester of the triple
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
and three fatty acids. The molecule of a triglyceride can be described as resulting from a
condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...
(specifically,
esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
) between each of glycerol's –OH groups and the HO– part of the carboxyl group of each fatty acid, forming an ester bridge with elimination of a water molecule . Other less common types of fats include diglycerides and
monoglyceride Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two differen ...
s, where the esterification is limited to two or just one of glycerol's –OH groups. Other alcohols, such as
cetyl alcohol Cetyl alcohol , also known as hexadecan-1-ol and palmityl alcohol, is a C-16 fatty alcohol with the formula CH3(CH2)15OH. At room temperature, cetyl alcohol takes the form of a waxy white solid or flakes. The name cetyl derives from the whale ...
(predominant in
spermaceti Spermaceti is a waxy substance found in the head cavities of the sperm whale (and, in smaller quantities, in the oils of other whales). Spermaceti is created in the spermaceti organ inside the whale's head. This organ may contain as much as of ...
), may replace glycerol. In the
phospholipid Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
s, one of the fatty acids is replaced by
phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
or a monoester thereof. The benefits and risks of various amounts and types of dietary fats have been the object of much study, and are still highly controversial topics.


Essential fatty acids

There are two
essential fatty acid Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic ac ...
s (EFAs) in human nutrition:
alpha-Linolenic acid ''alpha''-Linolenic acid (ALA), also known as α-Linolenic acid (from Greek ''alpha'' meaning "first" and ''linon'' meaning flax), is an ''n''−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed, wa ...
(an
omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
) and
linoleic acid Linoleic acid (LA) is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this acid. ...
(an
omega-6 fatty acid Omega-6 fatty acids (also referred to as ω-6 fatty acids or ''n''-6 fatty acids) are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the ''n''-6 position, that is, the sixth bond, counting from ...
). The adult body can synthesize other lipids that it needs from these two.


Dietary sources


Saturated vs. unsaturated fats

Different foods contain different amounts of fat with different proportions of saturated and unsaturated fatty acids. Some animal products, like
beef Beef is the culinary name for meat from cattle (''Bos taurus''). In prehistoric times, humankind hunted aurochs and later domesticated them. Since that time, numerous breeds of cattle have been bred specifically for the quality or quantit ...
and
dairy products Dairy products or milk products, also known as lacticinia, are food products made from (or containing) milk. The most common dairy animals are cow, water buffalo, nanny goat, and ewe. Dairy products include common grocery store food items in ...
made with whole or reduced fat milk like
yogurt Yogurt (; , from tr, yoğurt, also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as ''yogurt cultures''. Fermentation of sugars in the milk by these bac ...
,
ice cream Ice cream is a sweetened frozen food typically eaten as a snack or dessert. It may be made from milk or cream and is flavoured with a sweetener, either sugar or an alternative, and a spice, such as cocoa or vanilla, or with fruit such as ...
,
cheese Cheese is a dairy product produced in wide ranges of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. During productio ...
and
butter Butter is a dairy product made from the fat and protein components of churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 80% butterfat. It is used at room temperature as a spread, melted as a condim ...
have mostly saturated fatty acids (and some have significant contents of
dietary cholesterol Cholesterol is any of a class of certain organic compound, organic molecules called lipids. It is a sterol (or chemical modification, modified steroid), a type of lipid. Cholesterol is biosynthesis, biosynthesized by all animal Cell (biology)# ...
). Other animal products, like
pork Pork is the culinary name for the meat of the domestic pig (''Sus domesticus''). It is the most commonly consumed meat worldwide, with evidence of pig husbandry dating back to 5000 BCE. Pork is eaten both freshly cooked and preserved ...
,
poultry Poultry () are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes (which includes chickens, qu ...
,
eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
, and seafood have mostly unsaturated fats. Industrialized
baked goods Baking is a method of preparing food that uses dry heat, typically in an oven, but can also be done in hot ashes, or on hot stones. The most common baked item is bread but many other types of foods can be baked. Heat is gradually transferred ...
may use fats with high unsaturated fat contents as well, especially those containing
partially hydrogenated oil Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic co ...
s, and
processed food Convenience food, also called tertiary processed food, is food that is commercially prepared (often through processing) to optimise ease of consumption. Such food is usually ready to eat without further preparation. It may also be easily p ...
s that are deep-fried in
hydrogenated oil Fat hydrogenation is the process of combining fat – typically liquid vegetable oils – with hydrogen, to convert some or all of the unsaturated fat into saturated fat, resulting in a solid or semi-solid fat. Changing the degree of saturation ...
are high in saturated fat content. Plants and fish oil generally contain a higher proportion of unsaturated acids, although there are exceptions such as
coconut oil frameless , right , alt = A cracked coconut and a bottle of coconut oil Coconut oil (or coconut butter) is an edible oil derived from the wick, meat, and milk of the coconut palm fruit. Coconut oil is a white solid fat; in warmer climates du ...
and
palm kernel oil Palm kernel oil is an edible plant oil derived from the kernel of the oil palm tree ''Elaeis guineensis''. It is related to other two edible oils: ''palm oil'', extracted from the fruit pulp of the oil palm, and ''coconut oil'', extracted from ...
. Foods containing unsaturated fats include
avocado The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family ( Lauraceae). It is native to the Americas and was first domesticated by Mesoamerican tribes more than 5,000 years ago. Then as now it was prized for ...
, nuts,
olive oil Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: ...
s, and
vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or f ...
s such as
canola Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, ...
. Many careful studies have found that replacing saturated fats with ''cis'' unsaturated fats in the diet reduces risk of
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, hea ...
s (CVDs),
diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
, or death. These studies prompted many medical organizations and public health departments, including the
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...
(WHO), to officially issue that advice. Some countries with such recommendations include: * United Kingdom * United States * India * Canada * Australia * Singapore * New Zealand * Hong Kong A 2004 review concluded that "no lower safe limit of specific saturated fatty acid intakes has been identified" and recommended that the influence of varying saturated fatty acid intakes against a background of different individual lifestyles and genetic backgrounds should be the focus in future studies. This advice is often oversimplified by labeling the two kinds of fats as ''bad fats'' and ''good fats'', respectively. However, since the fats and oils in most natural and traditionally processed foods contain both unsaturated and saturated fatty acids, the complete exclusion of saturated fat is unrealistic and possibly unwise. For instance, some foods rich in saturated fat, such as coconut and palm oil, are an important source of cheap dietary calories for a large fraction of the population in developing countries. Concerns were also expressed at a 2010 conference of the
American Dietetic Association The Academy of Nutrition and Dietetics is a 501(c)(6) trade association in the United States. With over 112,000 members, the association claims to be the largest organization of food and nutrition professionals. It has registered dietitian n ...
that a blanket recommendation to avoid saturated fats could drive people to also reduce the amount of polyunsaturated fats, which may have health benefits, and/or replace fats by refined carbohydrates — which carry a high risk of obesity and heart disease. For these reasons, the U.S.
Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
, for example, recommends to consume at least 10% (7% for high-risk groups) of calories from saturated fat, with an average of 30% (or less) of total calories from all fat. A general 7% limit was recommended also by the
American Heart Association The American Heart Association (AHA) is a nonprofit organization in the United States that funds cardiovascular medical research, educates consumers on healthy living and fosters appropriate cardiac care in an effort to reduce disability and deat ...
(AHA) in 2006. The WHO/FAO report also recommended replacing fats so as to reduce the content of myristic and palmitic acids, specifically. The so-called
Mediterranean diet The Mediterranean diet is a diet inspired by the eating habits of people who live near the Mediterranean Sea. When initially formulated in the 1960s, it drew on the cuisines of Greece, Italy, France and Spain. In decades since, it has also incor ...
, prevalent in many countries in the
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
area, includes more total fat than the diet of Northern European countries, but most of it is in the form of unsaturated fatty acids (specifically, monounsaturated and omega-3) from olive oil and fish, vegetables, and certain meats like lamb, while consumption of saturated fat is minimal in comparison. A 2017 review found evidence that a Mediterranean-style diet could reduce the risk of cardiovascular diseases, overall cancer incidence, neurodegenerative diseases, diabetes, and mortality rate. A 2018 review showed that a Mediterranean-like diet may improve overall health status, such as reduced risk of non-communicable diseases. It also may reduce the social and economic costs of diet-related illnesses. A small number of contemporary reviews have challenged this negative view of saturated fats. For example, an evaluation of evidence from 1966 to 1973 of the observed health impact of replacing dietary
saturated fat A saturated fat is a type of fat in which the fatty acid chains have all single bonds. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branche ...
with
linoleic acid Linoleic acid (LA) is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this acid. ...
found that it ''increased'' rates of death from all causes, coronary heart disease, and cardiovascular disease. These studies have been disputed by many scientists, and the consensus in the medical community is that saturated fat and cardiovascular disease are closely related. Still, these discordant studies fueled debate over the merits of substituting polyunsaturated fats for saturated fats.


Cardiovascular disease

The effect of saturated fat on cardiovascular disease has been extensively studied. The general consensus is that there is evidence of moderate-quality of a strong, consistent, and graded relationship between saturated fat intake, blood cholesterol levels, and the incidence of cardiovascular disease. The relationships are accepted as causal, including by many government and medical organizations. A 2017 review by the AHA estimated that replacement of saturated fat with polyunsaturated fat in the American diet could reduce the risk of cardiovascular diseases by 30%. The consumption of saturated fat is generally considered a risk factor for
dyslipidemia Dyslipidemia is an abnormal amount of lipids (e.g. triglycerides, cholesterol and/or fat phospholipids) in the blood. Dyslipidemia is a risk factor for the development of atherosclerotic cardiovascular disease ( ASCVD). ASCVD includes coronary ar ...
—abnormal blood lipid levels, including high total cholesterol, high levels of triglycerides, high levels of
low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densi ...
(LDL, "bad" cholesterol) or low levels of
high-density lipoprotein High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are t ...
(HDL, "good" cholesterol). These parameters in turn are believed to be risk indicators for some types of cardiovascular disease. These effects were observed in children too. Several
meta-analyses A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting m ...
(reviews and consolidations of multiple previously published experimental studies) have confirmed a significant relationship between saturated fat and high
serum cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membr ...
levels, which in turn have been claimed to have a causal relation with increased risk of cardiovascular disease (the so-called
lipid hypothesis The lipid hypothesis (also known as the cholesterol hypothesis) is a medical theory postulating a link between blood cholesterol levels and the occurrence of cardiovascular disease. A summary from 1976 described it as: "measures used to lower t ...
). However, high cholesterol may be caused by many factors. Other indicators, such as high LDL/HDL ratio, have proved to be more predictive. In a study of
myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which ma ...
in 52 countries, the
ApoB Apolipoprotein B (ApoB) is a protein that in humans is encoded by the gene. Function Apolipoprotein B is the primary apolipoprotein of chylomicrons, VLDL, Lp(a), IDL, and LDL particles (LDL—commonly known as "bad cholesterol" when in refer ...
/
ApoA1 Apolipoprotein AI (ApoA-I) is a protein that in humans is encoded by the ''APOA1'' gene. As the major component of HDL particles, it has a specific role in lipid metabolism. Structure ''APOA1'' is located on chromosome 11, with its specific lo ...
(related to LDL and HDL, respectively) ratio was the strongest predictor of CVD among all risk factors. There are other pathways involving
obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...
,
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...
levels, insulin sensitivity, endothelial function, and
thrombogenicity Thrombogenicity refers to the tendency of a material in contact with the blood to produce a thrombus, or clot. It not only refers to fixed thrombi but also to emboli, thrombi which have become detached and travel through the bloodstream. Thrombo ...
, among others, that play a role in CVD, although it seems, in the absence of an adverse blood lipid profile, the other known risk factors have only a weak
atherogenic Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no ...
effect. Different saturated fatty acids have differing effects on various lipid levels.


Cancer

The evidence for a relation between saturated fat intake and
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
is significantly weaker, and there does not seem to be a clear medical consensus about it. * A meta-analysis published in 2003 found a significant positive relationship between saturated fat and
breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or ...
. However two subsequent reviews have found weak or insignificant relation, and noted the prevalence of confounding factors. * Another review found limited evidence for a positive relationship between consuming animal fat and incidence of
colorectal cancer Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum (parts of the large intestine). Signs and symptoms may include blood in the stool, a change in bowel ...
. * Other meta-analyses found evidence for increased risk of
ovarian cancer Ovarian cancer is a cancerous tumor of an ovary. It may originate from the ovary itself or more commonly from communicating nearby structures such as fallopian tubes or the inner lining of the abdomen. The ovary is made up of three different ...
by high consumption of saturated fat. * Some studies have indicated that serum
myristic acid Myristic acid (IUPAC name: tetradecanoic acid) is a common saturated fatty acid with the molecular formula CH3(CH2)12COOH. Its salts and esters are commonly referred to as myristates or tetradecanoates. It is named after the binomial name for nut ...
and
palmitic acid Palmitic acid (hexadecanoic acid in IUPAC nomenclature) is a fatty acid with a 16-carbon chain. It is the most common saturated fatty acid found in animals, plants and microorganisms.Gunstone, F. D., John L. Harwood, and Albert J. Dijkstra. The ...
and dietary myristic and palmitic saturated fatty acids and serum palmitic combined with alpha-tocopherol supplementation are associated with increased risk of
prostate cancer Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that su ...
in a dose-dependent manner. These associations may, however, reflect differences in intake or metabolism of these fatty acids between the precancer cases and controls, rather than being an actual cause.


Bones

Various animal studies have indicated that the intake of saturated fat has a negative effect on effects on the mineral density of bones. One study suggested that men may be particularly vulnerable.


Disposition and overall health

Studies have shown that substituting monounsaturated fatty acids for saturated ones is associated with increased daily physical activity and resting energy expenditure. More physical activity, less anger, and less irritability were associated with a higher-oleic acid diet than one of a
palmitic acid Palmitic acid (hexadecanoic acid in IUPAC nomenclature) is a fatty acid with a 16-carbon chain. It is the most common saturated fatty acid found in animals, plants and microorganisms.Gunstone, F. D., John L. Harwood, and Albert J. Dijkstra. The ...
diet.


Monounsaturated vs. polyunsaturated fat

Assuming that unsaturated fatty acids (UFAs) are generally healthier than saturated ones (SFAs), another question that has gained attention in recent decades is the risks and benefits of monounsaturated fatty acids (MUFAs, with a single double bond) versus polyunsaturated fatty acids (PUFAs, with two or more double bonds). The most common fatty acids in human diet are unsaturated or mono-unsaturated. Monounsaturated fats are found in animal flesh such as red
meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
, whole milk products, nuts, and high fat fruits such as olives and avocados. Olive oil is about 75% monounsaturated fat. The high oleic variety
sunflower oil Sunflower oil is the non-volatile oil pressed from the seeds of the sunflower (''Helianthus annuus''). Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient. Sunflower oil is primarily composed o ...
contains at least 70% monounsaturated fat.
Canola oil Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, ...
and
cashew The cashew tree (''Anacardium occidentale'') is a tropical evergreen tree native to South America in the genus ''Anacardium'' that produces the cashew seed and the cashew apple accessory fruit. The tree can grow as tall as , but the dwarf cul ...
s are both about 58% monounsaturated fat.
Tallow Tallow is a rendered form of beef or mutton fat, primarily made up of triglycerides. In industry, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain technical criteria, includ ...
(beef fat) is about 50% monounsaturated fat. and
lard Lard is a semi-solid white fat product obtained by rendering the fatty tissue of a pig.Lard
entry in the ...
is about 40% monounsaturated fat. Other sources include
hazelnut The hazelnut is the fruit of the hazel tree and therefore includes any of the nuts deriving from species of the genus '' Corylus'', especially the nuts of the species ''Corylus avellana''. They are also known as cobnuts or filberts according ...
, avocado oil, macadamia nut oil, grapeseed oil, groundnut oil (
peanut oil Peanut oil, also known as groundnut oil or arachis oil, is a vegetable oil derived from peanuts. The oil usually has a mild or neutral flavor but, if made with roasted peanuts, has a stronger peanut flavor and aroma. It is often used in Americ ...
),
sesame oil Sesame oil is an edible vegetable oil derived from sesame seeds. The oil is one of the earliest-known crop-based oils. Worldwide mass modern production is limited due to the inefficient manual harvesting process required to extract the oil. ...
,
corn oil Corn oil (North American) or maize oil (British) is oil extracted from the germ of corn (maize). Its main use is in cooking, where its high smoke point makes refined corn oil a valuable frying oil. It is also a key ingredient in some margar ...
,
popcorn Popcorn (also called popped corn, popcorns or pop-corn) is a variety of corn kernel which expands and puffs up when heated; the same names also refer to the foodstuff produced by the expansion. A popcorn kernel's strong hull contains the se ...
,
whole grain A whole grain is a grain of any cereal and pseudocereal that contains the endosperm, germ, and bran, in contrast to refined grains, which retain only the endosperm. As part of a general healthy diet, consumption of whole grains is associated ...
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
,
cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more food ...
,
oatmeal Oatmeal is a preparation of oats that have been de-husked, steamed, and flattened, or a coarse flour of hulled oat grains (groats) that have either been milled (ground) or steel-cut. Ground oats are also called white oats. Steel-cut oats a ...
,
almond oil The almond (''Prunus amygdalus'', syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of this tree. Within the genus ' ...
,
sunflower oil Sunflower oil is the non-volatile oil pressed from the seeds of the sunflower (''Helianthus annuus''). Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient. Sunflower oil is primarily composed o ...
,
hemp oil Hemp oil (hemp seed oil) is oil obtained by pressing hemp seeds. Cold pressed, unrefined hemp oil is dark to clear light green in color, with a nutty flavor. The darker the color, the grassier the flavour. It should not be confused with hash oi ...
, and tea-oil camellia. Polyunsaturated fatty acids can be found mostly in nuts, seeds, fish, seed oils, and
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...
s. Food sources of polyunsaturated fats include:


Insulin resistance and sensitivity

MUFAs (especially oleic acid) have been found to lower the incidence of
insulin resistance Insulin resistance (IR) is a pathological condition in which cells fail to respond normally to the hormone insulin. Insulin is a hormone that facilitates the transport of glucose from blood into cells, thereby reducing blood glucose (blood sugar ...
; PUFAs (especially large amounts of
arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''ara ...
) and SFAs (such as
arachidic acid Arachidic acid, also known as icosanoic acid, is a saturated fatty acid with a 20-carbon chain. It is a minor constituent of cupuaçu butter (7%), perilla oil (0–1%), peanut oil (1.1–1.7%), corn oil (3%),U.S. Department of Agriculture, Agri ...
) increased it. These ratios can be indexed in the
phospholipid Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
s of human
skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...
and in other tissues as well. This relationship between dietary fats and insulin resistance is presumed secondary to the relationship between insulin resistance and
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...
, which is partially modulated by dietary fat ratios ( Omega-3/ 6/ 9) with both omega 3 and 9 thought to be anti-inflammatory, and omega 6 pro-inflammatory (as well as by numerous other dietary components, particularly
polyphenols Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...
and exercise, with both of these anti-inflammatory). Although both pro- and anti-inflammatory types of fat are
biologically Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
necessary, fat dietary ratios in most US diets are skewed towards Omega 6, with subsequent disinhibition of inflammation and potentiation of insulin resistance. This is contrary to the suggestion of more recent studies, in which polyunsaturated fats are shown to be protective against insulin resistance. The large scale KANWU study found that increasing MUFA and decreasing SFA intake could improve insulin sensitivity, but only when the overall fat intake of the diet was low. However, some MUFAs may promote
insulin resistance Insulin resistance (IR) is a pathological condition in which cells fail to respond normally to the hormone insulin. Insulin is a hormone that facilitates the transport of glucose from blood into cells, thereby reducing blood glucose (blood sugar ...
(like the SFAs), whereas PUFAs may protect against it.


Cancer

Levels of oleic acid along with other MUFAs in red blood cell membranes were positively associated with breast cancer risk. The saturation index (SI) of the same membranes was inversely associated with breast cancer risk. MUFAs and low SI in erythrocyte membranes are predictors of postmenopausal breast cancer. Both of these variables depend on the activity of the enzyme delta-9 desaturase (Δ9-d). Results from observational clinical trials on PUFA intake and cancer have been inconsistent and vary by numerous factors of cancer incidence, including gender and genetic risk. Some studies have shown associations between higher intakes and/or blood levels of omega-3 PUFAs and a decreased risk of certain cancers, including breast and colorectal cancer, while other studies found no associations with cancer risk.


Pregnancy disorders

Polyunsaturated fat supplementation was found to have no effect on the incidence of pregnancy-related disorders, such as
hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high b ...
or
preeclampsia Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease ...
, but may increase the length of
gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pr ...
slightly and decreased the incidence of early premature births. Expert panels in the United States and Europe recommend that pregnant and lactating women consume higher amounts of polyunsaturated fats than the general population to enhance the DHA status of the fetus and newborn.


"Cis fat" vs. "trans fat"

In nature, unsaturated fatty acids generally have double bonds in ''cis'' configuration (with the adjacent C–C bonds on the same side) as opposed to ''trans''. Nevertheless, ''trans'' fatty acids (TFAs) occur in small amounts in meat and milk of
ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
s (such as cattle and sheep), typically 2–5% of total fat. Natural TFAs, which include conjugated linoleic acid (CLA) and vaccenic acid, originate in the
rumen The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment al ...
of these animals. CLA has two double bonds, one in the ''cis'' configuration and one in ''trans'', which makes it simultaneously a ''cis''- and a ''trans''-fatty acid. Concerns about ''trans'' fatty acids in human diet were raised when they were found to be an unintentional byproduct of the partial hydrogenation of vegetable and fish oils. While these ''trans'' fatty acids (popularly called "trans fats") are edible, they have been implicated in many health problems. The hydrogenation process, invented and patented by
Wilhelm Normann Wilhelm Normann (16 January 1870, in Petershagen – 1 May 1939, in Chemnitz) (sometimes also spelled ''Norman'') was a German chemist who introduced the hydrogenation of fats in 1901, creating what later became known as trans fats. This inventi ...
in 1902, made it possible to turn relatively cheap liquid fats such as
whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
or
fish oil Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), precursors of certain eicosanoids that are known to reduce inflammation in the b ...
into more solid fats and to extend their shelf-life by preventing rancidification. (The source fat and the process were initially kept secret to avoid consumer distaste.) This process was widely adopted by the food industry in the early 1900s; first for the production of
margarine Margarine (, also , ) is a spread used for flavoring, baking, and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The spread was or ...
, a replacement for butter and shortening, and eventually for various other fats used in snack food, packaged baked goods, and deep fried products. Full hydrogenation of a fat or oil produces a fully saturated fat. However, hydrogenation generally was interrupted before completion, to yield a fat product with specific melting point, hardness, and other properties. Partial hydrogenation turns some of the ''cis'' double bonds into ''trans'' bonds by an
isomerization reaction In chemistry, isomerization or isomerisation is the process in which a molecule, polyatomic ion or molecular fragment is transformed into an isomer with a different chemical structure. Enolization is an example of isomerization, as is tautomeri ...
. The trans configuration is favored because it is the lower energy form. This side reaction accounts for most of the ''trans'' fatty acids consumed today, by far. An analysis of some industrialized foods in 2006 found up to 30% "trans fats" in artificial shortening, 10% in breads and cake products, 8% in cookies and crackers, 4% in salty snacks, 7% in cake frostings and sweets, and 26% in margarine and other processed spreads. Another 2010 analysis however found only 0.2% of trans fats in margarine and other processed spreads. Up to 45% of the total fat in those foods containing man-made ''trans'' fats formed by partially hydrogenating plant fats may be ''trans'' fat. Baking shortenings, unless reformulated, contain around 30% ''trans'' fats compared to their total fats. High-fat dairy products such as butter contain about 4%. Margarines not reformulated to reduce ''trans'' fats may contain up to 15% ''trans'' fat by weight, but some reformulated ones are less than 1% trans fat. High levels of TFAs have been recorded in popular "fast food" meals. An analysis of samples of
McDonald's McDonald's Corporation is an American multinational fast food chain, founded in 1940 as a restaurant operated by Richard and Maurice McDonald, in San Bernardino, California, United States. They rechristened their business as a hambur ...
French fries collected in 2004 and 2005 found that fries served in New York City contained twice as much trans fat as in
Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Cr ...
, and 28 times as much as in
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of Denmark , establish ...
, where trans fats are restricted. For
Kentucky Fried Chicken KFC (Kentucky Fried Chicken) is an American fast food restaurant chain headquartered in Louisville, Kentucky, that specializes in fried chicken. It is the world's second-largest restaurant chain (as measured by sales) after McDonald's, wit ...
products, the pattern was reversed: the Hungarian product containing twice the trans fat of the New York product. Even within the United States, there was variation, with fries in New York containing 30% more trans fat than those from
Atlanta Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,7 ...
.


Cardiovascular disease

Numerous studies have found that consumption of TFAs increases risk of cardiovascular disease. The
Harvard School of Public Health The Harvard T.H. Chan School of Public Health is the public health school of Harvard University, located in the Longwood Medical Area of Boston, Massachusetts. The school grew out of the Harvard- MIT School for Health Officers, the nation's firs ...
advises that replacing TFAs and saturated fats with ''cis'' monounsaturated and polyunsaturated fats is beneficial for health. Consuming trans fats has been shown to increase the risk of
coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pl ...
in part by raising levels of low-density lipoprotein (LDL, often termed "bad cholesterol"), lowering levels of high-density lipoprotein (HDL, often termed "good cholesterol"), increasing triglycerides in the bloodstream and promoting systemic inflammation. The primary health risk identified for trans fat consumption is an elevated risk of
coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pl ...
(CAD). A 1994 study estimated that over 30,000 cardiac deaths per year in the United States are attributable to the consumption of trans fats. By 2006 upper estimates of 100,000 deaths were suggested. A comprehensive review of studies of trans fats published in 2006 in the
New England Journal of Medicine ''The New England Journal of Medicine'' (''NEJM'') is a weekly medical journal published by the Massachusetts Medical Society. It is among the most prestigious peer-reviewed medical journals as well as the oldest continuously published one. His ...
reports a strong and reliable connection between trans fat consumption and CAD, concluding that "On a per-calorie basis, trans fats appear to increase the risk of CAD more than any other macronutrient, conferring a substantially increased risk at low levels of consumption (1 to 3% of total energy intake)". The major evidence for the effect of trans fat on CAD comes from the
Nurses' Health Study The Nurses Health Study is a series of prospective studies that examine epidemiology and the long-term effects of nutrition, hormones, environment, and nurses' work-life on health and disease development. The studies have been among the largest in ...
– a
cohort study A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing ...
that has been following 120,000 female nurses since its inception in 1976. In this study, Hu and colleagues analyzed data from 900 coronary events from the study's
population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction usi ...
during 14 years of followup. He determined that a nurse's CAD risk roughly doubled (
relative risk The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association be ...
of 1.93, CI: 1.43 to 2.61) for each 2% increase in trans fat calories consumed (instead of carbohydrate calories). By contrast, for each 5% increase in saturated fat calories (instead of carbohydrate calories) there was a 17% increase in risk (
relative risk The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association be ...
of 1.17, CI: 0.97 to 1.41). "The replacement of saturated fat or trans unsaturated fat by cis (unhydrogenated) unsaturated fats was associated with larger reductions in risk than an isocaloric replacement by carbohydrates." Hu also reports on the benefits of reducing trans fat consumption. Replacing 2% of
food energy Food energy is chemical energy that animals (including humans) derive from their food to sustain their metabolism, including their muscular activity. Most animals derive most of their energy from aerobic respiration, namely combining the carbohy ...
from trans fat with non-trans
unsaturated fat An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond ...
s more than halves the risk of CAD (53%). By comparison, replacing a larger 5% of food energy from saturated fat with non-trans unsaturated fats reduces the risk of CAD by 43%. Another study considered deaths due to CAD, with consumption of trans fats being linked to an increase in mortality, and consumption of
polyunsaturated fat Polyunsaturated fats are fats in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds. Polyunsaturated fat can be found mostly in nuts, seeds, fish, seed oils, and oysters. "Unsaturated" refers to the fact t ...
s being linked to a decrease in mortality. Trans fat has been found to act like saturated in raising the blood level of LDL ("bad cholesterol"); but, unlike saturated fat, it also decreases levels of HDL ("good cholesterol"). The net increase in LDL/HDL ratio with trans fat, a widely accepted indicator of risk for coronary artery disease, is approximately double that due to saturated fat. One randomized
crossover study In medicine, a crossover study or crossover trial is a longitudinal study in which subjects receive a sequence of different treatments (or exposures). While crossover studies can be observational studies, many important crossover studies are con ...
published in 2003 comparing the effect of eating a meal on blood lipids of (relatively) cis and trans-fat-rich meals showed that
cholesteryl ester 300px, Cholesterol oleate, a member of the cholesteryl ester family Cholesteryl ester, a dietary lipid, is an ester of cholesterol. The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl group of cholesterol. Chol ...
transfer (CET) was 28% higher after the trans meal than after the cis meal and that lipoprotein concentrations were enriched in
apolipoprotein Apolipoproteins are proteins that bind lipids (oil-soluble substances such as fats, cholesterol and fat soluble vitamins) to form lipoproteins. They transport lipids in blood, cerebrospinal fluid and lymph. The lipid components of lipoproteins ...
(a) after the trans meals. The citokyne test is a potentially more reliable indicator of CAD risk, although is still being studied. A study of over 700 nurses showed that those in the highest
quartile In statistics, a quartile is a type of quantile which divides the number of data points into four parts, or ''quarters'', of more-or-less equal size. The data must be ordered from smallest to largest to compute quartiles; as such, quartiles are a ...
of trans fat consumption had blood levels of
C-reactive protein C-reactive protein (CRP) is an annular (ring-shaped) pentameric protein found in blood plasma, whose circulating concentrations rise in response to inflammation. It is an acute-phase protein of hepatic origin that increases following interleukin- ...
(CRP) that were 73% higher than those in the lowest quartile.


Breast feeding

It has been established that ''trans'' fats in human
breast milk Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by mammary glands located in the breast of a human female. Breast milk is the primary source of nutrition for newborns, containing fat, protein, carbohydrates ( la ...
fluctuate with maternal consumption of trans fat, and that the amount of trans fats in the bloodstream of breastfed infants fluctuates with the amounts found in their milk. In 1999, reported percentages of trans fats (compared to total fats) in human milk ranged from 1% in Spain, 2% in France, 4% in Germany, and 7% in Canada and the United States.


Other health risks

There are suggestions that the negative consequences of trans fat consumption go beyond the cardiovascular risk. In general, there is much less scientific consensus asserting that eating trans fat specifically increases the risk of other chronic health problems: *
Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As ...
: A study published in Archives of Neurology in February 2003 suggested that the intake of both trans fats and saturated fats promotes the development of Alzheimer disease, although not confirmed in an animal model. It has been found that trans fats impaired memory and learning in middle-age rats. The brains of rats that ate trans-fats had fewer proteins critical to healthy neurological function. Inflammation in and around the hippocampus, the part of the brain responsible for learning and memory. These are the exact types of changes normally seen at the onset of Alzheimer's, but seen after six weeks, even though the rats were still young. *
Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
: There is no scientific consensus that consuming trans fats significantly increases cancer risks across the board. The American Cancer Society states that a relationship between trans fats and cancer "has not been determined." One study has found a positive connection between trans fat and prostate cancer. However, a larger study found a correlation between trans fats and a significant decrease in high-grade prostate cancer. An increased intake of trans fatty acids may raise the risk of breast cancer by 75%, suggest the results from the French part of the European Prospective Investigation into Cancer and Nutrition. *
Diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
: There is a growing concern that the risk of
type 2 diabetes Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urinatio ...
increases with trans fat consumption. However, consensus has not been reached. For example, one study found that risk is higher for those in the highest
quartile In statistics, a quartile is a type of quantile which divides the number of data points into four parts, or ''quarters'', of more-or-less equal size. The data must be ordered from smallest to largest to compute quartiles; as such, quartiles are a ...
of trans fat consumption. Another study has found no diabetes risk once other factors such as total fat intake and BMI were accounted for. *
Obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...
: Research indicates that trans fat may increase weight gain and abdominal fat, despite a similar caloric intake. A 6-year experiment revealed that monkeys fed a trans fat diet gained 7.2% of their body weight, as compared to 1.8% for monkeys on a mono-unsaturated fat diet. Although obesity is frequently linked to trans fat in the popular media, this is generally in the context of eating too many calories; there is not a strong scientific consensus connecting trans fat and obesity, although the 6-year experiment did find such a link, concluding that "under controlled feeding conditions, long-term TFA consumption was an independent factor in weight gain. TFAs enhanced intra-abdominal deposition of fat, even in the absence of caloric excess, and were associated with insulin resistance, with evidence that there is impaired post-insulin receptor binding signal transduction." * Infertility in women: One 2007 study found, "Each 2% increase in the intake of energy from trans unsaturated fats, as opposed to that from carbohydrates, was associated with a 73% greater risk of ovulatory infertility...". *
Major depressive disorder Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive low mood, low self-esteem, and loss of interest or pleasure in normally enjoyable activities. Intro ...
: Spanish researchers analysed the diets of 12,059 people over six years and found that those who ate the most trans fats had a 48 per cent higher risk of depression than those who did not eat trans fats. One mechanism may be trans-fats' substitution for
docosahexaenoic acid Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is a primary structural component of the human brain, cerebral cortex, skin, and retina. In physiological literature, it is given the name 22:6(n-3). It can be synthesized from alpha-lin ...
(DHA) levels in the
orbitofrontal cortex The orbitofrontal cortex (OFC) is a prefrontal cortex region in the frontal lobes of the brain which is involved in the cognitive process of decision-making. In non-human primates it consists of the association cortex areas Brodmann area 11, 1 ...
(OFC). Very high intake of trans-fatty acids (43% of total fat) in mice from 2 to 16 months of age was associated with lowered DHA levels in the brain (p=0.001). When the brains of 15 major depressive subjects who had committed suicide were examined post-mortem and compared against 27 age-matched controls, the suicidal brains were found to have 16% less (male average) to 32% less (female average) DHA in the OFC. The OFC controls reward, reward expectation, and
empathy Empathy is the capacity to understand or feel what another person is experiencing from within their frame of reference, that is, the capacity to place oneself in another's position. Definitions of empathy encompass a broad range of social, co ...
(all of which are reduced in depressive mood disorders) and regulates the
limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''P ...
. * Behavioral
irritability Irritability (also called as crankiness) is the excitatory ability that living organisms have to respond to changes in their environment. The term is used for both the physiological reaction to stimuli and for the pathological, abnormal or excessi ...
and
aggression Aggression is overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual; although it can be channeled into creative and practical outlets for some. It may occur either reacti ...
: a 2012 observational analysis of subjects of an earlier study found a strong relation between dietary trans fat acids and self-reported behavioral aggression and irritability, suggesting but not establishing causality. * Diminished
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remember ...
: In a 2015 article, researchers re-analyzing results from the 1999-2005 UCSD Statin Study argue that "greater dietary trans fatty acid consumption is linked to worse word memory in adults during years of high productivity, adults age <45". *
Acne Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...
: According to a 2015 study, trans fats are one of several components of Western pattern diets which promote acne, along with
carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
s with high
glycemic load The glycemic load (GL) of food is a number that estimates how much the food will raise a person's blood glucose level after eating it. One unit of glycemic load approximates the effect of eating one gram of glucose. Glycemic load accounts for how ...
such as refined sugars or refined starches,
milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modulat ...
and dairy products, and
saturated fat A saturated fat is a type of fat in which the fatty acid chains have all single bonds. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branche ...
s, while
omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
s, which reduce acne, are deficient in Western pattern diets.


Biochemical mechanisms

The exact
biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology an ...
process by which trans fats produce specific health problems are a topic of continuing research. Intake of dietary trans fat perturbs the body's ability to metabolize
essential fatty acid Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic ac ...
s (EFAs, including Omega-3) leading to changes in the phospholipid fatty acid composition of the arterial walls, thereby raising risk of coronary artery disease. Trans double bonds are claimed to induce a linear conformation to the molecule, favoring its rigid packing as in plaque formation. The geometry of the ''cis'' double bond, in contrast, is claimed to create a bend in the molecule, thereby precluding rigid formations.. While the mechanisms through which trans fatty acids contribute to coronary artery disease are fairly well understood, the mechanism for their effects on diabetes is still under investigation. They may impair the metabolism of long-chain polyunsaturated fatty acids (LCPUFAs). However, maternal pregnancy trans fatty acid intake has been inversely associated with LCPUFAs levels in infants at birth thought to underlie the positive association between breastfeeding and intelligence. Trans fats are processed by the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
differently than other fats. They may cause
liver dysfunction Liver disease, or hepatic disease, is any of many diseases of the liver. If long-lasting it is termed chronic liver disease. Although the diseases differ in detail, liver diseases often have features in common. Signs and symptoms Some of the s ...
by interfering with delta 6 desaturase, an
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
involved in converting essential fatty acids to
arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''ara ...
and
prostaglandin The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are deriv ...
s, both of which are important to the functioning of cells.


Natural "trans fats" in dairy products

Some ''trans'' fatty acids occur in natural fats and traditionally processed foods. Vaccenic acid occurs in breast milk, and some
isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...
of conjugated linoleic acid (CLA) are found in meat and dairy products from
ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
s. Butter, for example, contains about 3% trans fat. The U.S. National Dairy Council has asserted that the trans fats present in animal foods are of a different type than those in partially hydrogenated oils, and do not appear to exhibit the same negative effects. While a recent scientific review agrees with the conclusion (stating that "the sum of the current evidence suggests that the Public health implications of consuming trans fats from ruminant products are relatively limited"), it cautions that this may be due to the low consumption of trans fats from animal sources compared to artificial ones. More recent inquiry (independent of the dairy industry) has found in a 2008 Dutch meta-analysis that all trans fats, regardless of natural or artificial origin equally raise LDL and lower HDL levels. Other studies though have shown different results when it comes to animal-based trans fats like conjugated linoleic acid (CLA). Although CLA is known for its anticancer properties, researchers have also found that the cis-9, trans-11 form of CLA can reduce the risk for
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, hea ...
and help fight inflammation. Two Canadian studies have shown that vaccenic acid, a TFA that naturally occurs in dairy products, could be beneficial compared to hydrogenated vegetable
shortening Shortening is any fat that is a solid at room temperature and used to make crumbly pastry and other food products. Although butter is solid at room temperature and is frequently used in making pastry, the term ''shortening'' seldom refers to b ...
, or a mixture of pork lard and soy fat, by lowering total LDL and triglyceride levels. A study by the US Department of Agriculture showed that vaccenic acid raises both HDL and LDL cholesterol, whereas industrial trans fats only raise LDL with no beneficial effect on HDL.


Official recommendations

In light of recognized evidence and scientific agreement, nutritional authorities consider all trans fats equally harmful for health and recommend that their consumption be reduced to trace amounts. In 2003, the WHO recommended that trans fats make up no more than 0.9% of a person's diet and, in 2018, introduced a 6-step guide to eliminate industrially-produced trans-fatty acids from the global food supply. The
National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nat ...
(NAS) advises the U.S. and Canadian governments on nutritional science for use in public policy and product labeling programs. Their 2002 ''Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids'' contains their findings and recommendations regarding consumption of trans fat. Their recommendations are based on two key facts. First, "trans fatty acids are not essential and provide no known benefit to human health", whether of animal or plant origin. Second, given their documented effects on the LDL/HDL ratio, the NAS concluded "that dietary trans fatty acids are more deleterious with respect to coronary artery disease than saturated fatty acids". A 2006 review published in the
New England Journal of Medicine ''The New England Journal of Medicine'' (''NEJM'') is a weekly medical journal published by the Massachusetts Medical Society. It is among the most prestigious peer-reviewed medical journals as well as the oldest continuously published one. His ...
(NEJM) that states "from a nutritional standpoint, the consumption of trans fatty acids results in considerable potential harm but no apparent benefit." Because of these facts and concerns, the NAS has concluded there is no safe level of trans fat consumption. There is no adequate level, recommended daily amount or tolerable upper limit for trans fats. This is because any incremental increase in trans fat intake increases the risk of coronary artery disease. Despite this concern, the NAS dietary recommendations have not included eliminating trans fat from the diet. This is because trans fat is naturally present in many animal foods in trace quantities, and thus its removal from ordinary diets might introduce undesirable side effects and nutritional imbalances. The NAS has, thus, "recommended that trans fatty acid consumption be as low as possible while consuming a nutritionally adequate diet". Like the NAS, the WHO has tried to balance public health goals with a practical level of trans fat consumption, recommending in 2003 that trans fats be limited to less than 1% of overall energy intake.


Regulatory action

In the last few decades, there has been substantial amount of
regulation Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. ...
in many countries, limiting trans fat contents of industrialized and commercial food products.


Alternatives to hydrogenation

In recent years, the negative public image and strict regulations have driven many fat processing industries to replace partial hydrogenation by
fat interesterification In the food industry and biochemistry, interesterification (IE) is a process that rearranges the fatty acids of a fat product, typically a mixture of triglyceride. The process implies breaking and reforming the ester bonds C–O–C that connec ...
, a process that chemically scrambles the fatty acids among a mix of triglycerides. When applied to a suitable bend of oils and saturated fats, possibly followed by separation of unwanted solid or liquid triglycerides, this process can achieve results similar to those of partial hydrogenation without affecting the fatty acids themselves; in particular, without creating any new "trans fat". Researchers at the
U.S. Department of Agriculture The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...
have investigated whether hydrogenation can be achieved without the side effect of trans fat production. They varied the
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...
under which the chemical reaction was conducted – applying 1400  kPa (200  psi) of pressure to soybean oil in a 2-liter vessel while heating it to between 140 °C and 170 °C. The standard 140 kPa (20 psi) process of hydrogenation produces a product of about 40% trans fatty acid by weight, compared to about 17% using the high-pressure method. Blended with unhydrogenated liquid soybean oil, the high-pressure-processed oil produced margarine containing 5 to 6% trans fat. Based on current U.S. labeling requirements (see below), the manufacturer could claim the product was free of trans fat. The level of trans fat may also be altered by modification of the temperature and the length of time during hydrogenation. A
University of Guelph , mottoeng = "to learn the reasons of realities" , established = May 8, 1964 ()As constituents: OAC: (1874) Macdonald Institute: (1903) OVC: (1922) , type = Public university , chancellor ...
research group has found a way to mix oils (such as olive, soybean, and canola), water,
monoglyceride Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two differen ...
s, and fatty acids to form a "cooking fat" that acts the same way as trans and saturated fats.


Omega-three and omega-six fatty acids

The ω−3 fatty acids have received substantial attention in recent years. Among omega-3 fatty acids, neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels of
docosahexaenoic acid Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is a primary structural component of the human brain, cerebral cortex, skin, and retina. In physiological literature, it is given the name 22:6(n-3). It can be synthesized from alpha-lin ...
(DHA), however, the most abundant omega-3
polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This class includes many important compounds, such as essential fatty acids and those that give drying oils their characteristic proper ...
in erythrocyte (
red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hol ...
) membranes, were associated with a reduced risk of breast cancer. The DHA obtained through the consumption of polyunsaturated fatty acids is positively associated with cognitive and behavioral performance. In addition, DHA is vital for the
grey matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil ( dendrites and unmyelinated axons), glial cells ( astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is ...
structure of the human brain, as well as retinal stimulation and
neurotransmission Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), ...
.


Interesterification

Some studies have investigated the health effects of insteresterified (IE) fats, by comparing diets with IE and non-IE fats with the same overall fatty acid composition. Several experimental studies in humans found no statistical difference on fasting blood lipids between a diet with large amounts of IE fat, having 25-40% C16:0 or C18:0 on the 2-position, and a similar diet with non-IE fat, having only 3-9% C16:0 or C18:0 on the 2-position. A negative result was obtained also in a study that compared the effects on blood
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
levels of an IE fat product mimicking
cocoa butter Cocoa butter, also called theobroma oil, is a pale-yellow, edible fat extracted from the cocoa bean. It is used to make chocolate, as well as some ointments, toiletries, and pharmaceuticals. Cocoa butter has a cocoa flavor and aroma. Its melt ...
and the real non-IE product. A 2007 study funded by the Malaysian Palm Oil Board claimed that replacing natural
palm oil Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced fr ...
by other interesterified or partially hydrogenated fats caused adverse health effects, such as higher LDL/ HDL ratio and
plasma glucose level Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood plas ...
s. However, these effects could be attributed to the higher percentage of saturated acids in the IE and partially hydrogenated fats, rather than to the IE process itself.


Role in disease

In the human body, high levels of triglycerides in the bloodstream have been linked to
atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no s ...
,
heart disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...
and
stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...
. However, the relative negative impact of raised levels of triglycerides compared to that of LDL:HDL ratios is as yet unknown. The risk can be partly accounted for by a strong inverse relationship between triglyceride level and HDL-cholesterol level. But the risk is also due to high triglyceride levels increasing the quantity of small, dense LDL particles.


Guidelines

The
National Cholesterol Education Program {{Primary sources, article, date=May 2011The National Cholesterol Education Program is a program managed by the National Heart, Lung and Blood Institute, a division of the National Institutes of Health. Its goal is to reduce increased cardiovascula ...
has set guidelines for triglyceride levels: These levels are tested after
fasting Fasting is the abstention from eating and sometimes drinking. From a purely physiological context, "fasting" may refer to the metabolic status of a person who has not eaten overnight (see " Breakfast"), or to the metabolic state achieved after ...
8 to 12 hours. Triglyceride levels remain temporarily higher for a period after eating. The AHA recommends an optimal triglyceride level of 100mg/dL (1.1mmol/L) or lower to improve heart health.


Reducing triglyceride levels

Weight loss and dietary modification are effective first-line lifestyle modification treatments for hypertriglyceridemia. For people with mildly or moderately high levels of triglycerides, lifestyle changes, including weight loss, moderate exerciseCrawford, H., Micheal. ''Current Diagnosis & Treatment Cardiology''. 3rd ed. McGraw-Hill Medical, 2009. p21 and dietary modification, are recommended. This may include restriction of carbohydrates (specifically
fructose Fructose, or fruit sugar, is a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorb ...
) and fat in the
diet Diet may refer to: Food * Diet (nutrition), the sum of the food consumed by an organism or group * Dieting, the deliberate selection of food to control body weight or nutrient intake ** Diet food, foods that aid in creating a diet for weight loss ...
and the consumption of
omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
s from algae, nuts, fish and seeds. Medications are recommended in those with high levels of triglycerides that are not corrected with the aforementioned lifestyle modifications, with
fibrate In pharmacology, the fibrates are a class of amphipathic carboxylic acids and esters. They are derivatives of fibric acid (phenoxyisobutyric acid). They are used for a range of metabolic disorders, mainly hypercholesterolemia (high cholesterol), ...
s being recommended first. Omega-3-carboxylic acids is another prescription drug used to treat very high levels of blood triglycerides. The decision to treat hypertriglyceridemia with medication depends on the levels and on the presence of other risk factors for cardiovascular disease. Very high levels that would increase the risk of pancreatitis are treated with a drug from the
fibrate In pharmacology, the fibrates are a class of amphipathic carboxylic acids and esters. They are derivatives of fibric acid (phenoxyisobutyric acid). They are used for a range of metabolic disorders, mainly hypercholesterolemia (high cholesterol), ...
class.
Niacin Niacin, also known as nicotinic acid, is an organic compound and a form of vitamin B3, an essential human nutrient. It can be manufactured by plants and animals from the amino acid tryptophan. Niacin is obtained in the diet from a variet ...
and omega-3 fatty acids as well as drugs from the
statin Statins, also known as HMG-CoA reductase inhibitors, are a class of lipid-lowering medications that reduce illness and mortality in those who are at high risk of cardiovascular disease. They are the most common cholesterol-lowering drugs. Low ...
class may be used in conjunction, with statins being the main medication for moderate hypertriglyceridemia when reduction of cardiovascular risk is required.


Fat digestion and metabolism

Fats are broken down in the healthy body to release their constituents,
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
and
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...
s. Glycerol itself can be converted to
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
by the liver and so become a source of energy. Fats and other lipids are broken down in the body by enzymes called
lipase Lipase ( ) is a family of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually ...
s produced in the
pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an ...
. Many cell types can use either glucose or fatty acids as a source of energy for metabolism. In particular, heart and skeletal muscle prefer fatty acids. Despite long-standing assertions to the contrary, fatty acids can also be used as a source of fuel for brain cells through mitochondrial oxidation.


See also

*
Animal fat Animal fats and oils are lipids derived from animals: oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides. Although many animal parts and secretions may yield oil, in commerci ...
* Diet and heart disease *
Fatty acid synthesis In biochemistry, fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes called fatty acid synthases. This process takes place in the cytoplasm of the cell. Most of the acetyl-CoA which is co ...
* Food composition data * Western pattern diet


References

{{Authority control Nutrients Macromolecules