Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults

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Abstract
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 overweight or obese [body mass index (in kg/m2): 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 × 10−4 mmol·kg−1·min−1 per pmol/L; 95% CI: 0.003 × 10−4, 0.144 × 10−4). Conclusion: Insulin sensitivity may be an important mechanism whereby whole-grain foods reduce the risk of type 2 diabetes and heart disease.