Piece of chocolate cake on a white plate decorated with chocolate sauce

Appetite is the desire to eat food items, usually due to

hunger In politics, humanitarian aid, and the social sciences, hunger is defined as a condition in which a person does not have the physical or financial capability to eat sufficient food to meet basic nutritional needs for a sustained period. In t ...

. Appealing foods can stimulate appetite even when hunger is absent, although appetite can be greatly reduced by satiety. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain

metabolic Metabolism (, from ''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 cellular processes; the ...

needs. It is regulated by a close interplay between the

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

adipose tissue Adipose tissue (also known as body fat or simply fat) is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, Blood vessel, vascular endothel ...

and the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. Appetite has a relationship with every individual's behavior. Appetitive behaviour also known as approach behaviour, and consummatory behaviour, are the only processes that involve energy intake, whereas all other behaviours affect the release of energy. When stressed, appetite levels may increase and result in an increase of food intake. Decreased desire to eat is termed anorexia, while

polyphagia Polyphagia, or hyperphagia, is an abnormally strong, wikt:incessant, incessant sensation of Hunger (physiology), hunger or desire to eat often leading to overeating. In contrast to an increase in appetite following exercise, polyphagia does not s ...

(or "hyperphagia") is increased eating. Dysregulation of appetite contributes to ARFID,

anorexia nervosa Anorexia nervosa (AN), often referred to simply as anorexia, is an eating disorder characterized by Calorie restriction, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. Individuals wit ...

bulimia nervosa Bulimia nervosa, also known simply as bulimia, is an eating disorder characterized by binge eating (eating large quantities of food in a short period of time, often feeling out of control) followed by compensatory behaviors, such as self-indu ...

cachexia Cachexia () is a syndrome that happens when people have certain illnesses, causing muscle loss that cannot be fully reversed with improved nutrition. It is most common in diseases like cancer, Heart failure, congestive heart failure, chronic o ...

, overeating, and

binge eating disorder Binge eating disorder (BED) is an eating disorder characterized by frequent and recurrent binge eating episodes with associated negative psychological and social problems, but without the compensatory behaviors common to bulimia nervosa, OSFE ...

Role in disease

A limited or excessive appetite is not necessarily pathological. Abnormal appetite could be defined as eating habits causing

malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is a deficiency, excess, or imbalance of energy, protein and other nutrients which adversely affects the body's tissues a ...

and related conditions such as

obesity Obesity is a medical condition, considered by multiple organizations to be a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it can potentially have negative effects on health. People are classifi ...

and its related problems. Both genetic and environmental factors may regulate appetite, and abnormalities in either may lead to abnormal appetite. Poor appetite ( anorexia) can have a number of causes, but may be a result of physical (infectious, autoimmune or malignant disease) or psychological (stress, mental disorders) factors. Likewise, hyperphagia (excessive eating) may be a result of hormonal imbalances, mental disorders (e.g., depression) and others. Dyspepsia, also known as indigestion, can also affect appetite as one of its symptoms is feeling "overly full" soon after beginning a meal.

Taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

and smell (" dysgeusia", bad taste) or the lack thereof may also affect appetite. Abnormal appetite may also be linked to genetics on a chromosomal scale, shown by the 1950s discovery of

Prader–Willi syndrome Prader–Willi syndrome (PWS) is a rare genetic disorder caused by a loss of function of specific genes on chromosome 15. In newborns, symptoms include hypotonia, weak muscles, poor feeding, and slow development. Beginning in childhood, those ...

, a type of obesity caused by chromosome alterations. Additionally, anorexia nervosa and bulimia nervosa are more commonly found in females than males – thus hinting at a possibility of a linkage to the X-chromosome.

Eating disorders

Dysregulation of appetite lies at the root of

, and

. Anorexia nervosa is a mental disorder characterized as severe dietary restriction and intense fear of weight gain. Furthermore, persons with anorexia nervosa may exercise ritualistically. Individuals who have anorexia have high levels of ghrelin, a hormone that stimulates appetite, so the body is trying to cause hunger, but the urge to eat is being suppressed by the person. Binge eating disorder (commonly referred to as BED) is described as eating excessively (or uncontrollably) between periodic time intervals. The risk for BED can be present in children and most commonly manifests during adulthood. Studies suggest that the heritability of BED in adults is approximately 50%. Similarly to bulimia, some people may be involved in purging and binging. They might vomit after food intake or take purgatives.

Body dysmorphic disorder Body dysmorphic disorder (BDD), also known in some contexts as dysmorphophobia, is a mental disorder defined by an overwhelming preoccupation with a perceived flaw in one's physical appearance. In BDD's delusional variant, the flaw is imagined ...

may involve food restriction in an attempt to deal with a perceived fault, and may be associated with depression and social isolation.

Obesity

Various hereditary forms of obesity have been traced to defects in hypothalamic signaling (such as the leptin receptor and the MC-4 receptor) or are still awaiting characterization – Prader-Willi syndrome – in addition, decreased response to satiety may promote development of

. It has been found that ghrelin-reactive IgG immunoglobulins affect ghrelin's orexigenic response. Other than genetically stimulated appetite abnormalities, there are physiological ones that do not require genes for activation. For example, ghrelin and

leptin Leptin (from Ancient Greek, Greek λεπτός ''leptos'', "thin" or "light" or "small"), also known as obese protein, is a protein hormone predominantly made by adipocytes (cells of adipose tissue). Its primary role is likely to regulate long ...

are released from the stomach and adipose cells, respectively, into the blood stream. Ghrelin stimulates feelings of hunger, whereas leptin stimulates feelings of satisfaction from food. Any changes in normal production levels of these two hormones can lead to obesity. The amount of leptin hormone production is stimulated by body fat percentage. When body fat accumulates there is overproduction of leptin causing a resistant hypothalamus and eventually almost no leptin effect. From then all ghrelin production causes insatiable appetite.

Pediatric eating problems

Eating issues such as " picky eating" affects about 25% of children, but among children with development disorders this number may be significantly higher, which in some cases may be related to the sounds, smells, and tastes (

sensory processing disorder Sensory processing disorder (SPD), formerly known as sensory integration dysfunction, is a condition in which multisensory input is not adequately processed in order to provide appropriate responses to the demands of the environment. Sensory ...

Pharmacology and treatment

The

glycemic index The glycemic (glycaemic) index (GI; ) is a number from 0 to 100 assigned to a food, with pure glucose arbitrarily given the value of 100, which represents the relative rise in the blood glucose level two hours after consuming that food. The GI of ...

is thought to affect satiety; however a study investigating the effect of satiety found that the glycemic index of foods did not predict effects on satiety and food intake.

Suppression

Mechanisms controlling appetite are a potential target for weight loss drugs. Appetite control mechanisms seem to strongly counteract undereating, whereas they appear weak to control overeating. Early anorectics (appetite suppressants) were fenfluramine and phentermine. A more recent addition is sibutramine which increases

serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...

and noradrenaline levels in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

, but had to be withdrawn from the market when it was shown to have an adverse cardiovascular risk profile. Similarly, the appetite suppressant rimonabant (a cannabinoid receptor antagonist) had to be withdrawn when it was linked with worsening depression and increased risk of suicide. Recent reports on recombinant PYY 3-36 suggest that this agent may contribute to

weight loss Weight loss, in the context of medicine, health, or physical fitness, refers to a reduction of the total body mass, by a mean loss of fluid, body fat (adipose tissue), or lean mass (namely bone mineral deposits, muscle, tendon, and other conn ...

by suppressing appetite. Given the epidemic proportions of

in the Western world and the fact that it is increasing rapidly in some poorer countries, observers expect developments in this area to snowball in the near future.

Stimulation

Weight loss or loss of appetite ("

") is an effect of some diseases, and a side effect of some

prescription drug A prescription drug (also prescription medication, prescription medicine or prescription-only medication) is a pharmaceutical drug that is permitted to be dispensed only to those with a medical prescription. In contrast, over-the-counter drugs c ...

s. Stimulants such as

methylphenidate Methylphenidate, sold under the brand names Ritalin ( ) and Concerta ( ) among others, is a central nervous system (CNS) stimulant used in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It may be taken Oral adm ...

commonly reduce appetite in patients, and have been prescribed off-label for weight loss. Three agents are approved for appetite stimulation in the United States: megestrol acetate - a

progesterone Progesterone (; P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...

available as an oral tablet, oxandrolone - an oral

anabolic steroid Anabolic steroids, also known as anabolic-androgenic steroids (AAS), are a class of drugs that are structurally related to testosterone, the main male sex hormone, and produce effects by binding to the androgen receptor (AR). Anabolism, Anaboli ...

, and dronabinol - THC, the principal

cannabinoid Cannabinoids () are several structural classes of compounds found primarily in the ''Cannabis'' plant or as synthetic compounds. The most notable cannabinoid is the phytocannabinoid tetrahydrocannabinol (THC) (delta-9-THC), the primary psychoact ...

marijuana Cannabis (), commonly known as marijuana (), weed, pot, and ganja, List of slang names for cannabis, among other names, is a non-chemically uniform psychoactive drug from the ''Cannabis'' plant. Native to Central or South Asia, cannabis has ...

, available in an oral capsule. Ghrelin, a gut hormone recognized as affecting appetite, is under investigation. Ghrelin itself must be delivered parenterally and research has therefore focused on substances that can be taken orally. Rikkunshito, a traditional Japanese Kampo medicine, is under preliminary research for its potential to stimulate ghrelin and appetite.

References

{{Authority control Endocrinology Eating behaviors