A body shape index (ABSI) reflects body composition changes in response to testosterone treatment in obese men.

BACKGROUND: Interventions such as testosterone treatment may change body composition and metabolic outcomes without substantial changes in weight and BMI.

OBJECTIVES: Using testosterone treatment as a paradigm, we hypothesized that a body shape index (ABSI) reflects body composition changes more accurately than traditional markers, such as weight, BMI and waist circumference.

INTERVENTION: Secondary analysis of a 56-week RCT in 100 dieting obese men with low-normal testosterone receiving testosterone treatment or placebo, and subsequent off-treatment follow-up.

RESULTS: At the end of the trial period, ABSI-unlike weight, BMI or waist circumference-had significantly decreased in the treatment group, compared with placebo (mean adjusted difference -0.18 [95% CI: -0.32, -0.05] × 10-2 m11/6 kg-2/3 , overall P<0.001). Changes in ABSI during the active trial phase correlated with changes in fat mass (tau = 0.18, P = 0.02), and not with lean mass (tau = -0.11, P = 0.14), BMI (tau = 0.10, P = 0.17), or visceral fat (tau = 0.07, P = 0.37). ABSI baseline values were positively correlated with waist circumference (tau = 0.21, P = 0.002) and visceral fat (tau = 0.18, P = 0.009), correlated inversely with lean mass (tau = -0.21, P = 0.002), and were uncorrelated with BMI (tau = -0.10, P = 0.15) and fat mass (tau = 0.01, P = 0.83). Two years after cessation of treatment, ABSI again reflected body composition as the between-group differences in all parameters did not persist.

CONCLUSIONS: A readily obtainable anthropomorphic measure, ABSI reflects the differential loss of fat mass mediated by testosterone in dieting obese men more closely than BMI or waist circumference. It may serve as a clinically useful marker to monitor body composition changes, particularly in response to interventions.