Whole grains are seeds that have not been milled or refined to remove the bran and germ. Most whole grains are grass seeds, although the term includes some foods that are not technically grains.
Whole grains are essential components of a healthy diet. They are important sources of:
Dietary fiber is believed to be responsible for at least some of the health benefits of whole grains, including a reduced risk for obesity, heart disease, and type 2 diabetes. Fiber provides a feeling of fullness with fewer calories. Soluble fiber helps reduce blood cholesterol levels. Insoluble fiber helps move waste through the digestive tract. Fiber can prevent or reduce constipation by keeping the stool soft and bulky. It can help prevent diverticular disease (the development of small pouches in the colon that become irritated and inflamed) by decreasing intestinal pressure. Fiber may help stimulate anticoagulants, which prevent the formation of small blood clots that can lead to heart attack or stroke.
Whole grains contain a multitude of phytonutrients in various combinations. Some evidence suggests that when consumed in whole foods, anti-inflammatory phytonutrients in the bran and germ of whole grains may help protect against chronic diseases such as cardiovascular disease and certain cancers. The effects of these phytonutrients may be additive or even synergistic with each other and with dietary fiber and minerals in whole grains, as well as complementing phytonutrients and fiber in fruits and vegetables when consumed together. Although the mechanisms of most phytonutrients are not known, plant sterols in whole grains inhibit cholesterol absorption and increase cholesterol secretion. Other phytonutrients in whole grains have antioxidant activities that may help protect against certain cancers, as well as preventing LDL cholesterol from reacting with oxygen, which may be a key step in the early development of cholesterol-clogged arteries. Whole grains contain hundreds of as-yet-unidentified phytochemicals that also may play important roles in human health.
Grains, also called cereals, are a staple food worldwide and constitute the largest portion of the world's food supply. Some form of grain is used in almost every meal. For many thousands of years, humans ate whole grain direct from the stalk. Even after they began grinding grain, all three layers of the grain seed—bran, endosperm, and germ—were utilized. The bran is the tough, fibrous, outer protective layer; the starchy endosperm provides stored energy for the reproductive kernel or germ inside; and the germ is rich in vitamins, minerals, and unsaturated oils.
Consumption of whole grains began to decline in the late nineteenth century with the invention of industrial rollers for milling. Milling removes the bran and germ and pulverizes the starchy endosperm. This makes the grain easier to chew and renders the starch much more accessible to the digestive system because the bran and fiber in whole grains impede the breakdown of starch to glucose. Milling also enables grains to be kept for long periods without refrigeration because it removes the oils in the germ that can go rancid and affect taste.
In addition to removing fiber and unsaturated oils, milling and refining remove a significant proportion of the phytonutrients, which are concentrated in the bran and inner germ layers. Although food processing, including milling and heating, can help release some phytonutrients from their bound forms, making them more available to the body, the human body has evolved its own mechanisms for releasing phytonutrients from whole grains. For example, an enzyme in the human intestine and in intestinal micro-flora releases ferulic acid from bran. Phenolic acids, such as ferulic acid, are among the most important phytonutrients in whole grains, with corn having the highest concentrations.
Wheat is the world's major cereal grain and the most popular grain in the United States. Wheat berries are the unprocessed seeds. The entire wheat grain is ground to produce 100% whole-wheat flour. Wheat berries are coarsely milled into smaller pieces to make cracked wheat; steamed, dried, and cracked to produce bulgur wheat; and steamed, dried, and flattened to make rolled wheat. Kamut is an ancient wheat with more nutritional value than modern hybridized wheat. Spelt is another nonhybridized wheat that is higher in protein and fiber than other strains of wheat. Nutritional values for a half-cup (138 mL) of cooked whole grains range from:
There are many other whole grains with different flavors and characteristics, including:
These grains vary in their nutritional content, with one-half cup (138 mL) of cooked whole grains ranging from:
Corn is a whole grain that is often eaten as a vegetable. As corn dries, its natural sugar turns to starch. Popcorn and whole-grain cornmeal are particularly nutritious. Yellow corn is the only grain with significant amounts of vitamin A. Blue corn has more protein, manganese, and potassium than white or yellow corn.
Rice is one of the most versatile grains, with readily usable protein. Brown rice is a whole grain with more protein, fiber, B vitamins, vitamin E, calcium, phosphorus, iron, and linoleic acid than polished white rice. Basmati rice is a long-grain, aromatic, white rice used in Indian cooking. Texmati or brown basmati rice is a cross between long-grain brown and basmati rice. Japonica is a short-grain black rice from Japan that is usually combined with brown rice in gourmet blends. Wild rice is the seed of an aquatic grass that is more closely related to corn than to rice and is more nutritious than conventional rice. The nutritional values for one-half cup (138 mL) of cooked rice vary from:
Buckwheat and amaranth are considered whole grains, even though they are not technically grains. Buckwheat is a member of the rhubarb family and is ground for flour or hulled for groats. Toasted buckwheat groats are called kasha. Amaranth seeds are an ancient Aztec food. One-half cup (138 mL) of cooked buckwheat groats has 103 calories, 23.8 g of carbohydrates, 0.8 g of fat, 2.4 g of fiber, and 4 g of protein; whereas amaranth has 122 calories, 21.5 g of carbohydrates, 2.1 g of fat, 4.9 g of fiber, and 4.7 g of protein.
Sprouted grains such as sprouted wheat, millet, barley, and rice are growing in popularity due to their potential health benefits. Because sprouted grains contain more water and germination standards vary, it is difficult to make nutritional comparisons between whole grains and sprouted grains.
Refined grains are usually enriched, meaning that some nutrients that are lost in processing are added back. Some countries require the enrichment of specific refined grains. At least some B vitamins may be added back because thiamin, riboflavin, and niacin are important for the metabolism of carbohydrates, fats, and proteins and are essential for nervous system function. Dietary fiber is not replaced, however. Enriched white rice is sprayed with a vitamin solution after milling and then coated with protein powder to replace a few of the lost nutrients.
“Fortified” means that nutrients have been added that do not occur naturally in that food. Many enriched grains are also fortified with other vitamins such as folic acid and minerals such as iron. Fortification with folate is particularly important, because this B vitamin helps prevent neural tube defects in a developing fetus. Whole grains also may be fortified.
Identifying whole-grain products can be difficult. Products advertised as containing whole grains often have only very small amounts. Whole grain is not the first ingredient in most breads, cereals, rolls, and crackers that are labeled as “made with” or “containing” whole grain. Other misleading labels include “multigrain,”“stoneground,”“100% wheat,”“cracked wheat,”“seven-grain,” and “bran.” These are usually not whole-grain products. Dark breads may have molasses or added coloring rather than whole grains. To ensure that a product is whole grain, whole grain should be listed at the top of the ingredient list, and the product should contain a high percent daily value (%DV) for fiber.
Less-processed whole grains contain more nutrients. For example, finely ground whole grain is more rapidly digested and raises blood sugar higher and faster than coarsely ground or intact whole grain. Steel-cut oats are preferable to instant oats due to their lower glycemic index, and whole-wheat berries are preferable to whole-wheat bread.
People who consume whole grains exclusively should ensure that they consume sufficient folic acid, because whole grains are not typically fortified with this B vitamin. Therefore, it is important to eat plenty of folate-rich foods such as fruits, vegetables, and legumes.
Whole and cracked grain kernels contain the oil-rich germ and are susceptible to rancidity. They should be purchased in small quantities and stored in airtight containers in a cool, dark, dry place for only up to six months.
Whole grain is safe for most people to use, although it may cause flatulence (gas) or stomach discomfort in some people if it hasn't been a regular part of the diet. Those who have gluten allergies or sensitivity could experience additional symptoms and will need to avoid certain grains.
High fiber grains such as wheat bran can increase the absorption of some medications, for example digoxin, so it is best to take oral medications one hour before or four hours after eating high fiber grains.
All forms of wheat, rye, and barley contain gluten. Amaranth has traces of gluten. Oats sometimes can be problematic because they may be processed in a facility with gluten. All other grains are gluten-free as long as they have been handled in a gluten-free environment.
Rice is one of the easiest grains to digest and a good choice for people with food allergies. Millet is also easily digested and considered one of the least allergenic grains. Kamut may be less allergenic than common wheat, and some people with wheat allergies do not react to spelt. Sprouted grains also may contain fewer allergens than whole grains.
Whole grains are conspicuously absent from the diets of most American children, accounting for only 14% of their total daily grain consumption. Only 39% of children meet dietary recommendations for fiber from all sources. Rice cereal has been a first sold food introduced to babies. Because of the concern about inorganic arsenic contamination, however, the FDA proposed an action level, or limit, of 100 parts per billion (ppb) for inorganic arsenic in infant rice cereal in April 2016.
See also Antioxidants ; Artificial preservatives ; Cancer-fighting foods ; Carbohydrates ; Fiber ; High-fiber diet .
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Margaret Alic, PhD