Refined grains have been significantly modified from their natural composition, in contrast to whole grains. The modification process generally involves the mechanical removal of

bran Bran, also known as miller's bran, is the component of a Cereal, cereal grain consisting of the hard layersthe combined aleurone and Fruit anatomy#Pericarp layers, pericarpsurrounding the endosperm. Maize, Corn (maize) bran also includes the p ...

and germ, either through grinding or selective sifting.

Overview

A refined grain is defined as having undergone a process that removes the bran, germ and husk of the grain and leaves the

endosperm The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the Embryo#Pla ...

, or starchy interior. Examples of refined grains include white bread, white flour, corn grits and

white rice White rice is milled rice that has had the husk, bran, and germ removed. This alters the flavor, texture and appearance of the seed; helps prevent spoilage (extends its storage life); and makes it easier to digest. After brown rice is milled ...

. Refined grains are milled which gives a finer texture and improved shelf life. Because the outer parts of the grain are removed and used for animal feed and non-food use, refined grains have been described as less sustainable than whole grains. After refinement of grains became prevalent in the early 20th-century, nutritional deficiencies (

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

, thiamin,

riboflavin Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved in ...

and niacin) became more common in the United States.Sizer, Frances; Whitney, Ellie. (2013). ''Nutrition: Concepts and Controversies''. Cengage Learning. pp. 125-126. Edelstein, Sari. (2019). ''Food Science: An Ecological Approach''. Jones & Bartlett Learning. p. 480-482. To correct this, the Congress passed the U.S. Enrichment Act of 1942 which requires that iron, niacin, thiamin and riboflavin have to be added to all refined grain products before they are sold. Folate (folic acid) was added in 1996. Refining grain includes mixing, bleaching, and brominating; additionally, folate, thiamin, riboflavin, niacin, and iron are added back in to nutritionally enrich the product. Enriched grains are refined grains that have been fortified with additional nutrients. Whole grains contain more

dietary fiber Dietary fiber (fibre in English in the Commonwealth of Nations, Commonwealth English) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical co ...

than refined grains. After processing, fiber is not added back to enriched grains. Enriched grains are nutritionally comparable to whole grains but only in regard to their added nutrients. Whole grains contain higher amounts of minerals including chromium,

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

selenium Selenium is a chemical element; it has symbol (chemistry), symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elem ...

, and

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

and vitamins such as

Vitamin B6 Vitamin B6 is one of the B vitamins, and is an essential nutrient for humans. The term essential nutrient refers to a group of six chemically similar compounds, i.e., "vitamers", which can be interconverted in biological systems. Its active f ...

and

Vitamin E Vitamin E is a group of eight compounds related in molecular structure that includes four tocopherols and four tocotrienols. The tocopherols function as fat-soluble antioxidants which may help protect cell membranes from reactive oxygen speci ...

. Whole grains also provide phytochemicals which enriched grains lack. In the case of

maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...

, the process of

nixtamalization Nixtamalization ( ) is a process for the preparation of maize (corn), or other cereal grain, grain, in which the grain is soaked and cooking, cooked in an alkaline solution, usually limewater (but sometimes aqueous alkali metal carbonates), ...

(a chemical form of refinement) yields a considerable improvement in the bioavailability of niacin, thereby preventing pellagra in diets consisting largely of maize products. Similar to whole grains, refined grains are a good source of starch, including

resistant starch Resistant starch (RS) is starch, including its degradation products, that escapes from digestion in the small intestine of healthy individuals. Resistant starch occurs naturally in foods, but it can also be added as part of dried raw foods, or u ...

Research

The dietary guidance of many countries is to replace refined grains with whole grains. The Dietary Guidelines for Americans (2020–2025) advises people to limit their intake of refined grains to be no more than half of total daily grain consumption.

Cardiovascular disease

The

American Medical Association The American Medical Association (AMA) is an American professional association and lobbying group of physicians and medical students. This medical association was founded in 1847 and is headquartered in Chicago, Illinois. Membership was 271,660 ...

have advised people to consume whole grains instead of refined grains to improve cardiovascular risk factors. A 2020 review of controlled trials that used the GRADE approach found that although whole grains have been shown to improve

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 density ...

and total cholesterol there is insufficient evidence to recommend "whole grains as opposed to refined grains for the prevention and treatment of CVD".

Obesity

There is no strong scientific evidence associating refined grains with

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 ...

Nutrition

References

External links

''The History of Bread'', UK Bakers Federation, 2002
{{Wheat Cereals Food science