Whole-grain intake and insulin sensitivity: The Insulin Resistance Atherosclerosis Study

Background: Increased intake of whole-grain foods has been related to a reduced risk of developing diabetes and heart disease. One underlying pathway for this relation may be increased insulin sensitivity. Objective: We assessed the relation between dietary intake of whole grain-containing foods and insulin sensitivity (S_I). Design: We evaluated data from the Insulin Resistance Atherosclerosis Study (IRAS Exam I, 1992-1994). Usual dietary intakes in 978 middle-aged adults with normal (67%) or impaired (33%) glucose tolerance were ascertained by using an interviewer-administered, validated food-frequency questionnaire. Whole-grain intake (servings per day) was derived from dark breads and high-fiber and cooked cereals. S_I was assessed by minimal model analyses of the frequently sampled intravenous-glucose-tolerance test. Fasting insulin was measured by using a radioimmunoassay. We modeled the relation of whole-grain intake to log(S_I + 1) and to log(insulin) by using multivariable linear regression. Results: On average, IRAS participants consumed 0.8 servings of whole grains/d. Whole-grain intake was significantly associated with S_I (β = 0.082. P = 0.0005) and insulin (β = -0.0646, P = 0.019) after adjustment for demographics, total energy intake and expenditure, smoking, and family history of diabetes. The addition of body mass index and waist circumference attenuated but did not explain the association with S_I. The addition of fiber and magnesium resulted in a nonsignificant association that is consistent with the hypothesis that these constituents account for some of the effect of whole grains on S_I. Conclusion: Higher intakes of whole grains were associated with increases in insulin sensitivity.