Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults

Background: Epidemiologic studies have found whole-grain intake to be inversely associated with the risk of type 2 diabetes and heart disease. Objective: We tested the hypothesis that whole-grain consumption improves insulin sensitivity in overweight and obese adults. Design: This controlled experiment compared insulin sensitivity between diets (55% carbohydrate, 30% fat) including 6-10 servings/d of breakfast cereal, bread, rice, pasta, muffins, cookies, and snacks of either whole or refined grains. Total energy needs were estimated to maintain body weight. Eleven over-weight or obese [body mass index (in kg/m(2)): 27-36] hyperinsulinemic adults aged 25-56 y participated in a randomized crossover design. At the end of each 6-wk diet period, the subjects consumed 355 mL (12 oz) of a Liquid mixed meal, and blood samples were taken over 2 h. The next day a euglycemic hyperinsulinemic clamp test was administered. Results: Fasting insulin was 10% lower during consumption of the whole-grain than during consumption of the refined-grain diet (mean difference: -15 +/- 5.5 pmol/L; P = 0.03). After the whole-grain diet, the area under the 2-h insulin curve tended to be lower (-8832 pmol(.)min/L; 95% CI: -18720, 1062) than after the refined-grain diet. The rate of glucose infusion during the final 30 min of the clamp test was higher after the whole-grain diet (0.07 X 10(-4) mmol(.)kg(-1.)min(-1) per pmol/L; 95% Cl: 0.003 X 10(-4), 0.144 X 10(-4)). Conclusion: Insulin sensitivity may be an important mechanism whereby whole-grain foods reduce the risk of type 2 diabetes and heart disease.