The Role of Whole Grains in Disease Prevention

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Abstract

Despite universal acceptance of the importance of whole grains in the diet, consumer knowledge of the benefits of whole grains and intake of these foods are low. This review summarizes the research supporting whole-grain consumption and gives practical suggestions about how to increase whole-grain intake. Whole-grain foods are valuable sources of nutrients that are lacking in the American diet, including dietary fiber, B vitamins, vitamin E, selenium, zinc, copper, and magnesium. Whole-grain foods also contain phytochemicals, such as phenolic compounds, that together with vitamins and minerals play important roles in disease prevention. The exact mechanisms linking whole grains to disease prevention are not known but may include gastrointestinal effects, antioxidant protection, and intake of phytoestrogens. Dietary intake studies indicate that consumption of whole grains is far less than the recommended intake of 3 servings a day, with an average daily intake of 1 or fewer servings a day. A new whole-grains health claim, allowed in July 1999 by the Food and Drug Administration, and inclusion of a whole-grain recommendation in the 2000 revision of the US Dietary Guidelines for Americans, should help increase whole-grain consumption. J Am Diet Assoc. 2001; 101:780–785.

Section snippets

What Are Whole Grains?

Commonly consumed grains in the United States include wheat, corn, oat, barley, and rye. Many other grains exist but are not typically consumed in the United States. Whole grains are made up of the endosperm, the germ, and the bran of the grain. The endosperm makes up about 80% of the whole grain, while the germ and bran components vary among different grains. Whole grains are cholesterol-free and low in fat, high in dietary fiber and vitamins (especially B-vitamins), and are good sources of

Consumption of Whole Grains

Food consumption surveys reveal that Americans eat far less than the currently recommended intake of 3 servings of whole grains per day, with an average daily intake of 1 or fewer servings a day (3). Studies show that health benefits may begin with consumption of a single serving of a whole-grain food per day (4). However, only 13% of Americans include 1 or more servings of whole grains in their diets each day and less than 0.5% consume a whole-grain cereal each day. Currently, only about 5% of

The Role of Whole Grains in Preventing Disease

Research has found health benefits of eating whole foods, including grains, fruits, and vegetables, but is less definitive about the benefits of consuming individual nutrients or phytochemicals. Among a large group of women, age 55 to 69 years, eating at least 1 serving a day of whole-grain foods significantly reduced the risk of death from all causes compared with women who ate almost no whole-grain products (5). In this particular study, dark breads and whole-grain breakfast cereals made up

Whole Grains and Cardiovascular Disease

Cardiovascular disease (CVD) is the leading cause of death and disability of both men and women in the United States. There is strong epidemiological and clinical evidence linking consumption of whole grains to a reduced risk for coronary heart disease (9). Morris et al (10) followed 337 subjects for 10 to 20 years and concluded that a reduction in heart disease risk was attributable to a higher intake of cereal fiber, while indicating soluble sources such as pectin and guar did not account for

Whole Grains and Blood Glucose

Whole grains are known to affect glucose and insulin responses, partly due to their slower rate of digestion (24). The glycemic index measures blood glucose response to a standard amount of a specific food. Intact whole grains of barley, rice, rye, oats, corn, buckwheat, and wheat, for example, have glycemic indexes of 36 to 81, with barley and oats having the lowest values (25). Foods with low glycemic indexes produce small rises in blood sugar and blood insulin. Among people with diabetes,

Other Chronic Diseases

Jacobs et al (5) assessed the relationship between whole-grain intake and all-cause mortality in the Iowa Women’s Health Study. There were striking inverse associations of whole-grain intake with risk of death. Unadjusted total mortality rates in the lowest to highest quintiles of whole-grain intake were 13.4, 10.3, 9.0, 7.9, and 9.2 per 1,000 person-years. Further analyses evaluated whether the association of whole-grain intake with total mortality could be attributed to dietary constituents

Clinical Studies

Few feeding studies have been conducted on the biological effects of whole grains. Bruce et al (31) fed 12 subjects with hyperlipidemia a diet high in whole and unrefined foods as compared with a refined diet. Subjects consumed the refined-food diet for the first 4 weeks of the study and then switched to the phytochemical-rich diet for 4 weeks. The phytochemical-rich diet included dried fruits, nuts, tea, whole-grain products, and more than 6 servings per day of fruits and vegetables. The

Improving Whole Grain Awareness and Consumption

Despite the body of evidence demonstrating the health benefits of eating whole grains, many consumers are unable to accurately identify whole-grain foods. Some health professionals, while aware that whole grains are an important part of a healthful diet, are unable to name specific health benefits associated with whole grains. There are two important educational approaches to increasing awareness of whole-grain foods and increasing their consumption: a whole-grain health claim on food labels,

Whole Grains Health Claim

As they are now defined, health claims authorized by the Food and Drug Administration are messages that inform consumers about currently recognized links between nutrition and disease reduction. Health claims were designed to make a major contribution toward improving health, but they can take more than a year to be approved because of the scientific review, the publication of a proposed rule, and the time for public comments, which are all mandated under the FDA’s 1993 final food labeling

Whole Grains and the Dietary Guidelines

The USDA Food Guide Pyramid, developed as a tool for nutrition education, recommends that 6 to 11 servings of grain foods, such as bread, cereal, rice and pasta, be the foundation of a healthful diet, but whole grains are not mentioned in the pyramid itself, only in the descriptive materials that accompany it.

One of the Dietary Guidelines recommends, “Choose a variety of grains daily, especially whole grains.” In counseling patients and clients about whole-grain intake, dietitians might find

Discussion

Evidence for the connection between whole grains and health benefits is strong. Based on epidemiological studies and biologically plausible mechanisms, scientific evidence shows that regular consumption of whole-grain foods reduces rates of CHD and several forms of cancer. It may also help regulate blood glucose levels. More research is needed on the mechanisms for this protection. Additionally, because certain components in whole grains may be most important in this protection, these compounds

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