Distinctive postprandial modulation of β cell function and insulin sensitivity by dietary fats:: monounsaturated compared with saturated fatty acids

Background: Exaggerated and prolonged postprandial triglyceride concentrations are associated with numerous conditions related to insulin resistance, including obesity, type 2 diabetes, and the metabolic syndrome. Although dietary fats profoundly affect postprandial hypertriglyceridemia, limited data exist regarding their effects on postprandial glucose homeostasis. Objective: We sought to determine whether postprandial glucose homeostasis is modulated distinctly by high-fat meals enriched in saturated fatty acids (SFAs) or monounsaturated fatty acids (MUFAs). Design: Normotriglyceridemic subjects with normal fasting glucose and normal glucose tolerance were studied. Blood samples were collected over the 8 h after ingestion of a glucose and triglyceride tolerance test meal (GTTTM) in which a panel of dietary fats with a gradual change in the ratio of MUFAs to SFAs was included. On 5 separate occasions, basal and postprandial concentrations of glucose, insulin, triglyceride, and free fatty acids (FFAs) were measured. Results: High-fat meals increased the postprandial concentrations of insulin, triglycerides, and FFAs, and they enhanced postprandial beta cell function while decreasing insulin sensitivity (as assessed with different model-based and empirical indexes: insulinogenic index, insulinogenic index/homeostasis model assessment of insulin resistance, area under the curve for insulin/area under the curve for glucose, homeostasis model assessment for beta cell function, and GTTTM-determined insulin sensitivity, oral glucose insulin sensitivity, and the postprandial Belfiore indexes for glycemia and blood FFAs. These effects were significantly ameliorated, in a direct linear relation, when MUFAs were substituted for SFAs. Conclusions: The data presented here suggest that beta cell function and insulin sensitivity progressively improve in the postprandial state as the proportion of MUFAs with respect to SFAs in dietary fats increases.