School of Medicine

Background : Obesity and poor cardiorespiratory fitness (CRF) are strong predictors of insulin resistance. The mechanisms underpinning the beneficial effects of CRF on insulin action, however, are not fully understood. Several weight loss intervention trials have suggested that while improving CRF is associated with better insulin sensitivity in adolescents and adults, this association is no longer significant with correction for indices of adiposity. A growing body of literature in the last decade also indicates that CRF with or without changes in BMI/waist circumference enhances insulin sensitivity and that overweight/obese individuals with an adequate level of CRF may consequently be at a reduced risk of diseases associated with insulin resistance. In this project, we investigate whether CRF and degree of obesity have independent associations with insulin resistance in overweight/obese women enrolled in a weight loss trial. Methods : The data are from the MENU Study (Diet Composition and Genetics: Effects on Weight, Inflammation and Biomarkers), a randomized clinical trial funded as part of the TREC initiative at UCSD (Trans-disciplinary Research on Energetics and Cancer (TREC) - NCI U54CA155435). The main objective of the MENU trial is to examine if different macronutrient compositions in the diet affect a differential weight loss response in 234 healthy obese women, depending on insulin resistance status. The current paper utilizes baseline data on the 98 women who are enrolled in the first cohort. The variables used for the current analysis include BMI and waist circumference (WC), as well as insulin sensitivity by HOMA (homeostasis model assessment) approach. CRF was assessed by measuring heart rate during recovery after a 3-minute stepping test. Linear regression models were used to examine associations between CRF, BMI and insulin sensitivity. Results : The findings indicated that CRF was associated with less insulin resistance, independent of BMI and WC. The present study, along with others in recent l.