Grains have been the “staff of life” for thousands of years, serving as a vital food source for humans. Until the last century grains were commonly eaten as whole grains. Advances in the milling and processing of grains allowed large scale separation and removal of the bran and germ, resulting in refined flour that consists only of the endosperm. Refined flour became popular because it produced baked goods with a softer texture and extended freshness. In the early 1940’s, enrichment to restore some B vitamins (thiamin, riboflavin, and niacin) and the mineral iron to refined flour began.1 Enrichment is defined as the addition of vitamins and minerals to restore nutrients to levels found in a food prior to storage, handling, and processing.2 In 1996, the U.S. Food and Drug Administration mandated the fortification of enriched grain products with folic acid to help women of childbearing age reduce the risk of having a pregnancy affected with a neural tube defect.3 Similar to the process of enriching foods, fortification also refers to the addition of nutrients, but of nutrients that were not originally present in a food.2
When a grain is refined, most of the bran and some of the germ is removed, resulting in losses of fiber, B vitamins, vitamin E, trace minerals, unsaturated fat, and about 75 percent of the phytochemicals. Compared to refined grains, most whole grains provide more protein, fiber and other traditional nutrients, including calcium, magnesium, and potassium, in addition to many phytochemicals.
Today, foods made with whole grains are recognized as important sources of nutrients including fiber, trace minerals, and certain vitamins. Additional health-promoting components and phytochemicals found in whole grains are not restored through traditional grain enrichment and fortification practices and are believed to play a key role in reducing risk of disease. Research shows that healthful diets rich in whole grain foods are helpful in reducing the risks of heart disease, certain types of cancer, and type 2 diabetes, and may also help in weight management.4
The 2005 Dietary Guidelines for Americans recommends eating at least three servings (equivalent to 3 ounces) of whole-grain products per day. This recommendation is based on research that links the greatest health benefits to three daily servings of whole grain foods.4
Definition and Intake of Whole Grains
A whole grain consists of the entire grain seed of a plant. This seed, also known as the kernel, is made up of three key parts: the bran, the germ, and the endosperm (see diagram: Anatomy of a Whole Grain Kernel). Whole grains may be eaten whole, cracked, split, flaked, or ground. Most often, they are milled into flour and used to make breads, cereals, pasta, crackers, and other grain-based foods. Regardless of how the whole grain is handled, a whole grain food product must deliver approximately the same relative proportions of bran, germ, and endosperm found in the original grain.5
A whole grain can be a complete food, such as oatmeal, brown rice, barley, or popcorn, or used as an ingredient in food, such as whole wheat flour in bread or cereal. Types of whole grains include whole wheat, whole oats/oatmeal, whole grain cornmeal, popcorn, brown rice, whole rye, whole-grain barley, wild rice, buckwheat, triticale, bulgur (cracked wheat), millet, quinoa, and sorghum. Other less common whole grains include amaranth, emmer, farro, grano (lightly pearled wheat), spelt, and wheat berries. According to the National Health and Nutrition Examination Survey (NHANES), only 35 percent of Americans age 12 and over met their total grain recommendation; 4 percent met the current whole grain recommendation.6
Effects of Whole Grains Beyond Fiber
Some research demonstrates that the health-promoting effects of whole grains are attributed to more than fiber. Studies show that in women even after controlling for fiber intake, the health effects of whole grains and heart disease remain.7 However, in men while the whole grain was protective for heart disease, the bran or fiber component of whole grains provided a significant portion of the protection.8 While fiber from whole grains is well-known to impart important health benefits, whole grains are more than a dietary vehicle for delivering fiber.
The fiber content of different whole-grain foods can vary considerably, between 0.5 and 4 grams of fiber per serving, depending on the food category and serving size.9 Some grain foods that contain a significant or high amount of fiber may not contain a significant amount of whole grain. For example, oat bran or high fiber bran cereals may contain very little or no whole grain, but provide high levels of fiber because they are made with only the bran portion of the grain.
The health advantages of whole grains are largely associated with consuming the entire whole grain “package,” which includes vitamins, minerals, essential fatty acids, phytochemicals and other bioactive food components.10,11 Phytochemicals are substances in plant-based foods with physiologically active components that have functional health benefits. Most of the health-promoting substances are found in the germ and bran of a grain kernel and include resistant starch, oligosaccharides, lignans, phytosterols, phytic acid, tannins, lipids, and antioxidants, such as phenolic acids and flavonoids.12
Although much of the research has focused on individual components of whole grains, such as fiber or antioxidants, epidemiological evidence suggests that the whole (grain) food offers protection against a wide range of diseases that is greater than what is seen with any individual component.13 The array of nutrients and other components in whole grains are believed to have an additive and synergistic effect on health.
Role of Grains in a Healthful Diet
The 2005 Dietary Guidelines for Americans recognizes refined and whole grains as important sources of carbohydrate. Carbohydrates supply energy to the body in the form of glucose, which is the only energy source for red blood cells and the preferred energy source for the brain, central nervous system, and during pregnancy, the placenta and fetus. Grains contain carbohydrate primarily in the form of starches and some fiber.
The Institute of Medicine (IOM) established a Recommended Dietary Allowance (RDA) for carbohydrates at 130 grams per day for adults and children.14 This is based on the minimum amount of carbohydrates (sugars and starches) required to provide the brain with an adequate supply of glucose. Muscle cells also rely on glucose during anaerobic (without oxygen) activity. If glucose is not available from the diet or the body’s storage form of glucose (glycogen) is depleted, the body will convert protein to glucose to supply the essential fuel to the brain and maintain blood glucose levels.14
The 2005 Dietary Guidelines for Americans advise at least half of an individual’s daily grain servings should come from whole grains with the remaining servings coming from enriched or whole-grain products.4 Folic acid fortification makes refined-grain products an important source of this B vitamin, which is associated with decreased risk of birth defects, including neural tube defects (NTD), and heart disease.15,16 With the exception of both hot and cold breakfast cereals, most whole-grain foods are not fortified with folic acid or other vitamins and minerals. This is one benefit to consuming refined enriched grain products.
Finding Whole Grain Foods
In general, a serving of grain is an ounce-equivalent of food, such as a slice of bread; a half cup of cooked cereal, rice, or pasta; or about 1 cup of dry cereal (¼ cup for dense, granola cereals to 1½ cups for some unsweetened puffed cereals). At least three ounce equivalents of whole grains per day are necessary to achieve the dietary recommendation of making half of you grains whole grains.4 Currently, the amount of whole grain present in a food product is allowed as a voluntary declaration, but is not required for whole grain foods. Although the number of whole-grain food choices is growing, consumers often believe they can identify whole grain products by name, color, or fiber content. Additional label reading is required to correctly identify foods that qualify as whole grain.
To verify that a product is whole grain, consumers should be encouraged to look beyond a product’s name. Descriptive words in the product's name, such as stone-ground, multi-grain, 100% wheat, or bran, do not necessarily indicate that a product is whole grain. Words to look for include “whole grain” or “100% whole wheat.”
Color and Texture:
The color of a food does not determine whole grain. Bread may be brown because molasses or caramel coloring has been added. Many whole-grain products, such as cereals, are light in color. Whole grain foods are not always dry or gritty, some whole-grain foods may be dense with a pleasant “nutty” flavor or light and flaky like a cereal grain.
The amount of fiber in a whole grain food varies depending on the type of grain, amount of bran, density of the product, and moisture content. Some whole grain foods may not be a “good” or “excellent” source of fiber. Labeling regulations allow a food to be called a good source of fiber if the food contains 2.5 to 4.9 grams of fiber per serving; an excellent source if it contains more than 4.9 grams per serving.17
The ingredient statement will list whole grains by the specific grain, such as whole wheat flour, whole oats, or whole grain corn. The phrase “whole grain” or “whole” will appear before the grain's name. In many whole grain foods, a whole grain is among the first ingredients listed. Foods made with several different whole grains noted further down on the list of ingredients may also qualify as a whole grain food. However, the ingredient list does not clearly indicate the amount of whole grain present in the food, nor does whole grain appear on the Nutrition Facts panel.
Based on Food and Drug Administration (FDA) regulations, a food manufacturer may choose to include a health claim that links a diet rich in whole grains to reduced risk of heart disease and some types of cancer. To qualify for this claim, a product must contain all portions of the grain kernel, contain at least 51 percent whole grain by weight per reference amount customarily consumed, and meet specified levels for fat, cholesterol, and sodium.18 A health claim might read, “Diets rich in whole-grain foods and other plant foods and low in total fat, saturated fat, and cholesterol may help reduce risk of heart disease and certain cancers.”
Innovations in the Food Supply
Food manufacturers are offering more options for consumers who want to increase their intake of whole grains. Recent consumer research conducted by the International Food Information Council Foundation shows that more than half of consumers (64%) are increasingly interested in consuming more whole grain foods.19 In response to the increase in consumer demand, food manufacturers are creating new products and reformulating existing products to contain increased levels of whole grains.
Some whole grain products are being made with "white wheat flour," which comes from a naturally occurring albino variety of wheat. This flour resembles typical refined flour, but it has the nutrition and fiber of whole wheat. White wheat does not contain tannins and phenolic acid, compounds found in the outer bran of the red wheat commonly used to make whole-wheat flour. In comparison, white wheat has a mild, sweet flavor more similar to that of a refined grain then a whole grain.
Another wheat flour offers the nutritional benefits of 100% whole wheat, yet functions and tastes like refined white flour. This flour is produced by a patented milling technique applied to traditional hard spring wheat, which preserves the mild flavor, color, and texture of refined flour.
Other traditional whole grains, such as oats and barley, are gaining popularity with consumers. In December 2005, the FDA added barley to the soluble fiber health claim. Certain products containing barley may now carry a claim that barley may reduce the risk of heart disease.20 Advances in technology have created a new barley product that is higher in total dietary fiber and lower in starch than traditional barley. Whole grain barley is also now available in a quick-cooking variety. Other innovative grain products have additional beneficial ingredients including oat-based products fortified with omega-3 fatty acids and vitamin E, and enriched pasta made with wheat, oats, spelt, legumes, and flaxseed.
Health Effects of Whole Grains
Research demonstrates an association between consuming whole grains as part of a low-fat diet and a reduced risk of heart disease. Studies have consistently found that individuals with three or more servings of whole grain foods per day have a 20 to 30 percent lower risk for atherosclerotic cardiovascular disease compared to individuals with lower intakes of whole grains.7,8,21-24 Researchers have also observed that diets rich in whole grain foods tend to decrease LDL cholesterol (the “bad” cholesterol), triglycerides, and blood pressure, and increase HDL cholesterol (the “good” cholesterol).25
Potential mechanisms for this health effect have been proposed, but are not fully understood. Components of some whole grains, including soluble fiber, beta glucan, alpha-tocotrienol, and the arginine-lysine ratio, are believed to play a role in lowering blood cholesterol. Whole grains may decrease risk of heart disease through their antioxidant content. Other bioactive components are believed to play a role in vascular reactivity, clotting, and insulin sensitivity.26-28 Although studies have not isolated the exact mechanisms for the positive effect of whole grains on cardiovascular health, it is likely that whole grain consumption is protective beyond what would be predicted if the effects of the individual components were simply additive.11,12
Whole grains appear to be associated with a reduced risk of a number of gastrointestinal cancers as well as several hormone-dependent cancers. A review of 40 studies on gastrointestinal cancers found a 21 to 43 percent lower cancer risk with high intake of whole grains compared to low intakes.21 Although studies examining the risk of hormone-dependent cancers are limited, the same review found that subjects in the highest category of whole grain intake had a 10 to 45 percent lower risk of endometrial cancer and a 37 to 40 percent lower risk for ovarian cancer.21
Whole grain foods may reduce the risk of cancer by a variety of mechanisms.29 Fiber and certain starches found in whole grains ferment in the colon to help reduce transit time and improve gastrointestinal health. Whole grains also contain antioxidants that may help protect against oxidative damage, which may play a role in cancer development. Other bioactive components in whole grains may affect hormone levels and possibly lower the risk of hormone dependent cancers. However, it remains unclear from current research what the association may be between whole grain intake and breast cancer risk.30
Components of whole grains, including fiber, resistant starch, and oligosaccharides play roles in supporting gastrointestinal health. Studies suggest that dietary fiber from whole grains such as wheat and oats increases stool weight.31 The increase in stool weight is caused by the presence of fiber, water that the fiber holds, and partial fermentation of fiber and oligosaccharides, which increases the amount of beneficial bacteria in stool.32 The large intestine responds to the larger and softer mass of residue produced by a higher fiber diet by contracting, which speeds the movement of the bowel contents towards excretion. The effect of promoting normal intestinal regularity makes whole- and high-fiber grain products integral components of diet plans to help alleviate constipation and decrease the risk of developing diverticulosis and diverticulitis.33
The American Diabetes Association Guidelines for the Prevention and Treatment of Diabetes recognizes the role of whole grains and fiber in reducing the risk of diabetes and maintenance of blood glucose levels.34 Major epidemiological studies show a reduced risk of 20 to 30 percent for type 2 diabetes associated with higher intakes of whole grain or cereal fiber.35 Evidence from observational studies and clinical trials suggests improved blood glucose control in people with diabetes and, in non-diabetic individuals, whole grains may lower fasting insulin levels and decrease insulin resistance.12,35 Components of whole grains, including magnesium, fiber, vitamin E, phytic acids, lectins, and phenolic compounds, are believed to contribute to risk reduction of type 2 diabetes as well as lowering blood glucose and blood insulin levels. In studies that examined the source of fiber, researchers found that fiber from whole grains, but not from fruit or vegetable sources, appears to exert the protective effect in reducing risk for developing type 2 diabetes.36-38
Emerging evidence suggests that whole grain intake may contribute to achieving and maintaining a healthy weight. Studies show that people who include whole grains as part of a healthful diet are less likely to gain weight over time.39-40 In a 12-year study, women who consumed more whole grains consistently weighed less than women who consumed fewer whole grains and those with the highest fiber intake had a lower risk of major weight gain.41 In men, whole grain and bran intake were independently related to less weight gain.40 In addition, whole grain intake is inversely associated with potential plasma biomarkers of obesity, including insulin, C-peptide, and leptin.42 The mechanisms by which whole grains may support weight management include enhanced satiety to lower energy intake, prolonged gastric emptying to delay the return of hunger, and increased insulin sensitivity to lower insulin demand.12,39
Whole grains contain many healthful components, including dietary fiber, starch, essential fatty acids, antioxidants, vitamins, minerals, lignans, and phenolic compounds, that have been linked to reduced risk of heart disease, cancer, diabetes, obesity, and other chronic diseases. Since most of the health-promoting components are found in the germ and bran, foods made with whole grains can play an important role in maintaining good health. When an adequate amount of whole grains are included in a healthful diet, there also is room for enriched grain food choices. Eating more whole grains involves making relatively easy changes in grain food selections. With awareness and education, along with increased availability of easy-to-identify whole-grain products, consumers can increase their intake of whole grains to recommended levels.
Functional Components of Whole Grains
Consist of the entire grain seed of a plant, including the bran, the germ, and the endosperm.
Whole wheat, whole oats/oatmeal, whole grain cornmeal, popcorn, brown rice, whole rye, whole grain barley, wild rice, buckwheat, triticale, bulgur (cracked wheat), millet, quinoa, and sorghum.
Functional Components of Certain Whole Grains:
Insoluble Fiber, Beta Glucan, Magnesium, Potassium, Selenium, Inulin, Thiamin (B1), Pyridoxine (B6)
Adapted from International Food Information Council Foundation: Media Guide on Food Safety and Nutrition: 2007-2009
Anatomy of a Whole Grain Kernel
Bran: The multi-layered outer skin of the kernel that helps to protect the other two parts of the kernel from sunlight, pests, water, and disease. It contains important antioxidants, iron, zinc, copper, magnesium, B vitamins, fiber, and phytonutrients.
Germ: The embryo, which, if fertilized by pollen, will sprout into a new plant. It contains B vitamins, vitamin E, antioxidants, phytonutrients, and unsaturated fats.
Endosperm: The germ's food supply, which, if the grain were allowed to grow would provide essential energy to the young plant. As the largest portion of the kernel, the endosperm contains starchy carbohydrates, proteins, and small amounts of vitamins and minerals.
Source for kernel diagram: http://wbc.agr.mt.gov/Consumers/diagram_kernel.html
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39. Koh-Banerjee P, Rimm EB. Whole-grain consumption and weight gain: a review of the epidemiological evidence, potential mechanisms and opportunities for future research. Proc Nutr Soc. 2003;62:25-29.
40. Koh-Banerjee P, Franz M, Sampson L, Liu S, Jacobs DRJ, Spiegelman D, Willett W, Rimm E. Changes in whole-grain, bran, and cereal fiber consumption in relation to 8-y weight gain among men. Am J Clin Nutr. 2004;80:1237-45.
41. Liu S, Willett WC, Manson JE, Hu FB, Rosner B, Colditz G. Relation between changes in intakes of dietary fiber and grain products and changes in weight and development of obesity among middle-aged women. Am J Clin Nutr. 2003;78:920-927.
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