Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort

OBJECTIVE - The aim of this study was to examine the relation between carbohydrate-related dietary factors, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort. RESEARCH DESIGN AND METHODS - We examined cross-sectional associations between carbohydrate-related dietary factors, insulin resistance, and the prevalence of the metabolic syndrome in 2,834 subjects at the fifth examination (1991-1995) of the Framingham Offspring Study. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated using the following formula (fasting plasma insulin X plasma glucose)/22.5. The metabolic syndrome was defined using the National Cholesterol Education Program criteria. RESULTS - After adjustment for potential confounding variables, intakes of total dietary fiber, cereal fiber, fruit fiber, and whole grains were inversely associated, whereas glycemic index and glycemic load were positively associated with HOMA-IR. The prevalence of the metabolic syndrome was significantly lower among those in the highest quintile of cereal fiber (odds ratio [OR] 0.62; 95% CI 0.45-0.86) and whole-grain (0.67; 0.48-0.91) intakes relative to those in the lowest quintile category after adjustment for confounding lifestyle and dietary factors. Conversely, the prevalence of the metabolic syndrome was significantly higher among individuals in the highest relative to the lowest quintile category of glycemic index (1.41; 1.04-1.91). Total carbohydrate, dietary fiber, fruit fiber, vegetable fiber, legume fiber, glycemic load, and refined grain intakes were not associated with prevalence of the metabolic syndrome. CONCLUSIONS - Whole-grain intake, largely attributed to the cereal fiber, is inversely associated with HOMA-IR and a lower prevalence of the metabolic syndrome. Dietary glycemic index is positively associated with HOMA-IR and prevalence of the metabolic syndrome. Given that both a high cereal fiber content and lower glycemic index are attributes of whole-grain foods recommendation to increase whole-grain intake may reduce the risk of developing the metabolic, syndrome.