Source: Tufts University
June 20, 2002 (Reviewed: June 29, 2004)Next time you’re asked if you want your sandwich on white or whole wheat, opt for latter. A new study from Harvard suggests that a diet that includes a variety of whole grain foods may decrease the risk of developing type 2 diabetes.
A closer look at diet
This study involved 11 overweight adults. All had higher than normal levels of insulin in their blood while in a fasting state, a warning sign of type 2 diabetes. They were randomly assigned to receive one of two diets. Both provided 55% of total calories from carbohydrate, 15% from protein, and 30% from fat, and both provided enough calories so the participants would neither gain nor lose weight during the study. But in one diet, all of the grain products – bread, cereal, and pasta – were made from whole grains. The other diet included grain foods made from refined white flour.
All participants followed one of the two diets for six weeks, and then switched to the other diet for an additional six weeks. The participants’ blood levels of insulin and glucose (fasting and after a standard meal) – were measured after completion of each diet. The participants also routinely completed questionnaires about the diets – whether they felt satisfied and liked the foods – as well as physical activity, medication use, gastrointestinal problems, and any unusual symptoms.
The researchers found that the whole grain diet helped the participants control their blood insulin levels better. Tests also showed that their bodies were better able to metabolize blood glucose, a step that keeps both insulin and glucose at healthier levels and may lower the risk of type 2 diabetes in those who do not yet have the disease.
Why did whole grains make a difference?
The authors of this study are not sure why whole grain foods seemed to help control blood insulin levels. Whole grains are high in fiber (which comes from both the outer bran layer and the nutrient-rich, inner germ level). Fiber slows the transit time of food through the gut and may help regulate the body’s release of insulin in response to a rise in blood sugar. The whole grain diet was also higher in vitamin E and magnesium than the refined grains diet; the study’s authors speculate that these nutrients might also have a metabolic effect on insulin levels.
Small changes
The profile of these study participants – overweight and “insulin resistant” – describes an ever-increasing number of adults in the United States and Europe; they are described as having the metabolic syndrome. Obviously, avoiding type 2 diabetes takes more than just switching from white to whole grain bread. The biggest culprits – excess weight and a sedentary lifestyle – call for prompt attention to one’s eating and exercise habits. The results of this study, though, show that small changes, such as choosing whole grain foods, can have a positive impact on health.
Is it really whole grain?
Whole grain foods will list the grain – whole wheat, oats, rye – as the first ingredient on the food label. Just because a bread is dark in color, for instance, does not mean that it is made from whole wheat. Check the label: it should say “whole wheat,” and not just “wheat.” Likewise for cereals and other grain foods.
Source:Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults. M. Pereira, D. Jacobs, J. Pins, et al., Am J Clin Nutr, 2002, vol.75, pp.848–855