(American Journal of Clinical Nutrition) -- Daily consumption of whole grains has been associated in a number of studies with reductions in risk for ischemic stroke, coronary artery disease, and type 2 diabetes. The cereal fiber found in whole grains slows digestion, producing a greater feeling of fullness and helping to prevent obesity, a major risk factor for type 2 diabetes. In a long-term study of male health professionals published in the American Journal of Clinical Nutrition, Fung et al. found that men who ate several servings of whole grains per day over a period of years had a substantially reduced risk of developing type 2 diabetes, and that some risk reduction occurred even in men who were obese.

Male health professionals, age 40-75 years without a history of diabetes or cardiovascular disease were recruited in 1986 and followed for 12 years. The 42,898 participants provided information on diet, health and lifestyle using questionnaires that were mailed to them every 2 years. The classification of "whole grains" included brown rice, dark breads, whole-grain ready-to-eat cereals, and other cereal foods. The subjects were divided into quintiles of whole grain consumption, with the lowest quintile eating 0.4 servings of whole grains per day and the highest quintile averaging 3.2 servings per day. Subjects with higher whole grain intakes tended to be leaner and more physically active, to consume less fat, and were less likely to smoke or have hypertension.

Between 1986 and 1998, 1197 cases of type 2 diabetes were diagnosed in the group. In comparison to those in the bottom quintile of whole grain intake, those in the top quintile had a 42% decreased risk for type 2 diabetes. Obese persons who were physically active and had high whole grain intakes had a 52% lower risk of diabetes than inactive obese persons in the lowest whole grain intake category. The high fiber content of the bran fraction of whole grains delays gastric emptying and slows the release of glucose into the circulation, thus reducing insulin response after meals. This process may also be responsible for lower obesity levels among high consumers of whole grains because a longer period of satiety follows meals. Magnesium, which has also been shown to improve glucose and insulin response, is present in higher amounts in whole grains than in refined grains.

The Dietary Guidelines for American 2000 specifically recommend choosing several servings of whole grains from among the recommended 6-11 servings of grains per day. Yet, whole grain intake is still far below that level for most Americans. The authors suggest that, especially in non-obese men, consumption of 3 servings of whole grains per day can substantially lower the incidence of type 2 diabetes.