The Association of Whole Grain Intake and Fasting Insulin in a Biracial Cohort of Young Adults: The CARDIA Study.

Background: Whole grain consumption may influence insulin through beneficial effects on satiety and body weight, intestinal absorption, or the action of specific nutrients or constituents.

Design and methods: We examined the associations of whole grain intake, assessed by a diet history interview at baseline (year 0) and year 7, with body mass index (BMI), waist-hip ratio (WHR), and fasting insulin in 3,627 Black and White adults in the Coronary Artery Risk Development in Young Adults Study (CARDIA). We estimated year 0 and year 7 cross-sectional associations accounting for correlation between years using repeated measures regression.

Results: After adjustment for age, education, energy intake, CARDIA field center, physical activity, alcohol consumption, and cigarette smoking, whole grain consumption was unrelated to WHR and inversely related to body mass index only in Whites at year 7. Whole grain consumption was inversely related to fasting insulin in Whites at year 0 and Black men and Whites at year 7. Mean differences for year 7 fasting insulin between the least vs. most frequent categories of whole grain consumption (0-2 vs. > 9 times/week) were 2.2, 1.0 and 1.0 μU/mL in Black men, white men, and white women, respectively (p < 0.05). The inverse association of whole grain intake and fasting insulin remained significant (p < 0.05) after adjustment for body mass index. Potentially mediating nutrients explaining part of the relationship between whole grain intake and fasting insulin were dietary magnesium and fiber.

Conclusions: The independent inverse relationship between whole grain consumption and fasting insulin levels may have important public health implications in light of the low consumption of whole grains and the increasing prevalence of obesity and diabetes in the US.