NEW YORK (Reuters Health) - Whole-grain foods, such as fiber-rich bread and bran cereal, may lower the risk of heart disease, type 2 diabetes and certain types of cancer by reducing cholesterol and making the body more responsive to insulin, researchers suggest.

In their study of close to 3,000 middle-aged adults, these foods were associated with lower levels of total cholesterol and LDL (the so-called "bad" cholesterol) and improved insulin sensitivity. Insulin, the body's key blood-sugar-regulating hormone, tends to be elevated in those at risk of type 2 diabetes.

People who consumed the most whole-grain foods also had a lower body mass index (BMI), a measure of weight in relation to height that is considered a more reliable gauge of overweight than weight alone. Indeed, adults who were overweight or obese had the highest insulin levels and consumed the least amount of whole-grain foods, researchers report in the August issue of the American Journal of Clinical Nutrition.

The findings help to explain how whole-grain foods may protect against several chronic disorders and point to the importance of including several daily servings of these foods in the diet. Current dietary guidelines recommend about nine daily servings of carbohydrates for adults, mostly in the form of whole-grain foods.

However, more research is needed into how carbohydrates affect insulin levels and obesity and the subsequent risk of type 2 diabetes and heart disease, Dr. Paul Jacques, the study's lead author, told Reuters Health.

Some health experts blame America's obesity epidemic on carbohydrates, pointing out that rates of obesity have risen in tandem with carbohydrate consumption over the past 30 years. Others argue that whole-grain foods, which are high in fiber, vitamin E and magnesium, do not have the same effect on insulin as refined carbohydrates that have been stripped of many nutrients.

"The importance of understanding the role of different carbohydrate sources in the development of insulin resistance is becoming even more critical because Americans appear to be increasing their intake of dietary carbohydrates," Jacques explained.

"Our results suggest that higher whole-grain intakes might help prevent development of insulin resistance, and the influence of whole grains may be strongest in those who are overweight and have the greatest risk of insulin resistance," he said.

The researchers analyzed detailed dietary information and blood samples from study volunteers over a 4-year period, and divided individuals into four groups according to their intake of whole-grain foods. Those with the highest intake of whole grains also tended to have healthier lifestyle habits such as moderate alcohol and meat consumption, not smoking, taking a multivitamin pill and eating lots of fruits and vegetables.

SOURCE: American Journal of Clinical Nutrition 2002;76:390-398.

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