Fitness Level is Associated with Sex-Specific Regional Fat Differences in Normal Weight Young Adults.

OBJECTIVES To characterize regional body composition and insulin sensitivity differences between young adults who were normal weight with either high or low fitness determined by VO2 peak. We hypothesized that higher fitness levels would be associated with reduced visceral fat (VAT) and improved insulin sensitivity. DESIGN A cross-sectional comparison of normal weight males and females with high or low fitness matched on age and sex. METHODS A total of 38 (20M/18F) individuals were recruited for this study. Thirty-two young adults (18M/14F) were matched on age (mean 22.5 ± 3 yrs.) and BMI (22.4 ± 2.4 kg/m2) and sex and classified by high or low fitness based on VO2 peak difference (≥ 8ml/kg/min). Total and regional body composition, including VAT, was measured by Dual Energy X-Ray Absorptiometry (DXA). Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. An analysis of variance compared regional body composition and insulin sensitivity between high and low fitness young adults with a normal BMI. RESULTS Higher fitness was associated with significantly lower percent body fat, lower android fat mass and higher insulin sensitivity in males (-7.2%, P<0.001; -0.5kg, P=0.048; 5.6mg/kg (FFM)/min, p=0.002). In females, higher fitness was associated with significantly lower percent body fat, lower leg fat but no difference in insulin sensitivity (-6.7%, P=0.001; -2.7kg, P<0.001; 2.5 mg/kg(FFM)/min, P=0.40). No differences in VAT were observed between high and low fitness groups. Interestingly in females, there was no difference in total lean mass, trunk lean mass or leg lean mass (P=0.59, P=0.17, P=0.99). CONCLUSION Higher fitness does not influence VAT in normal weight individuals. Sex influenced regional fat and insulin sensitivity differences between high fitness and low fitness groups.