Bran is the hard outer layer of Cereal grains, and consists of combined Aleurone and pericarp. Along with germ, it is an integral part of whole grains, and is often produced as a By-product of milling in the production of refined grains. Bran is present in and may be milled from any cereal grain, including Rice, Wheat, Maize, oats, and Millet.
Bran is particularly rich in Dietary fiber, and contains significant quantitities of Starch, Protein, Fat, vitamins, and dietary minerals. Oat bran, alone or as a part of Oatmeal, has been shown to reduce the risk of Coronary heart disease when part of an overall diet that is low in Saturated fat and Cholesterol, and the United States Food and Drug Administration now allows manufacturers to make specific health claims to that effect on food packaging. Wheat bran (miller's bran) is very effective in treating Constipation.
Bran is often used to enrich breads (notably muffins) and breakfast cereals, especially for the benefit of those wishing to increase their intake of dietary fiber. Bran may also be pickled, as in the Tsukemono of Japan.
Bran finds particularly many uses in Japan, where it is known as nuka (糠; ぬか). Besides pickling it, Japanese people also add it to the Water when Boiling bamboo shoots, and use it for dish washing.
The high oil content of bran makes it subject to Rancidification, one of the reasons that is often separated from the grain before storage or further processing. The bran itself can be heat-treated to increase its longevity.
Eating foods rich in bran became somewhat of a health craze in the late 1970s and early 1980s, with massive promotion of bran cereals and Granola. In the late 1980s, there was the "oat bran craze," with oat products in all shapes and sizes flooding the market (including Potato chips with oat bran added), claiming to lower blood Cholesterol and fight Heart disease. This craze peaked in 1989 and was short-lived, as studies in the early 1990s showed that oat bran only modestly reduced cholesterol. However, in January 1997, the Food and Drug Administration decided (with some persuading by Quaker Oats) that food with a lot of oat bran or rolled oats can carry a label claiming it may reduce the risk of heart disease, when combined with a low-fat diet. As of 2005, this fact still appears on many Oatmeal packages.
Bran oil may be also extracted for use by itself for industrial purposes (such as in the paint industry), or as a Cooking oil. Rice bran oil in particular is claimed to improve human health, as it contains oryzanol, an Antioxidant claimed to help prevent heart attacks.