Effect of high cardiorespiratory fitness and high body fat on insulin resistance

Purpose: High cardiorespiratory fitness (CRF) dramatically lowers risk for cardiometabolic disease in overweight and obese individuals. This effect is likely attributable to the inverse relationship between high CRF and insulin resistance. In this study, the independent effects of high body fat and high CRF on insulin resistance were assessed. Methods: The blood glucose and insulin responses to an oral glucose tolerance test were measured in 10 overweight women with high CRF (OF), 9 lean women with high CRF (LF), and 10 overweight women with low CRF (OU). Results: Fasting plasma glucose (P = 0.77), insulin (P = 0.23), and triacylglycerol (P = 0.99) concentrations were similar between OF and LF, with mean values in both groups lower than in OU. The glucose area under the curve (AUC) was not different between LF and OF (P = 0.28) and was significantly higher in OU. Insulin sensitivity, estimated from the composite insulin-sensitivity index (C-ISI), was slightly but significantly lower in OF compared with LF. Similarly, insulin AUC was 43% lower in LF compared with OF, although this difference was not statistically significant (P = 0.08). Insulin AUC was 50% higher (P = 0.04) and C-ISI was 35% lower (P = 0.09) in OU compared with OF. Conclusion: Compared with lean fit women, estimated insulin sensitivity was only slightly lower and plasma triacylglycerols were almost identical in overweight women with equally high CRF despite a,twofold elevation in body fat percentage.