Relationships between insulin sensitivity and measures of body fat in asymptomatic men and women

Objective: To assess whether measures of body fat by DXA scanning can improve prediction of insulin sensitivity (S-I) beyond what is possible with traditional measures, such as BMI, waist circumference, and waist-to-hip ratio (WHR). Research Methods and Procedures: Frequently sampled intravenous glucose tolerance tests were performed in 256 asymptomatic non-Hispanic white subjects from Rochester, MN (age 19-60 years; 123 men and 133 women) to determine the S-I index by Bergman's minimal model technique. Height, weight, and waist and hip circumferences were measured for calculation of BMI and WHR; DXA was used to determine fat in the head, upper body, abdomen, and lower body. Linear regression was used to assess their relationships with S-I after sex stratification and adjustment for age. Results: After controlling for age, increases in traditional and DXA measures of fat were consistently associated with smaller declines in S-I among women than among men. In men, after controlling for age, all of the predictive information of S-I was provided by waist circumference (additional R-2 = 0.39, p < 0.001); none of the DXA measures improved the ability to predict S-I. In women, after adjustment for age, BMI, and WHR, the only DXA measure that improved the prediction of S-I was percentage head fat (additional R-2 = 0.03, p < 0.001). Discussion: Equivalent increases in most measures of body fat had lesser impact on S-I in women than in men. In both sexes, the predictive information provided by DXA measures is approximately equal to, but not additive to, that provided by simpler, traditional measures.