Effects of pioglitazone versus diet and exercise on metabolic health and fat distribution in upper body obesity.

OBJECTIVE: Insulin resistance is associated with visceral adiposity, and interventions that reduce this depot, e.g., diet and exercise, improve insulin resistance. Thiazolidinediones (TZDs) also improve insulin action but paradoxically increase total fat mass, perhaps through remodeling (recruitment of smaller fat cells) and redistribution of adipose tissue. We assessed the effects of pioglitazone versus diet and exercise on fat distribution and the relationship between fat distribution and insulin sensitivity in upper body obesity.

RESEARCH DESIGN AND METHODS: Thirty-nine upper body obese, insulin-resistant, nondiabetic men and premenopausal women were randomly assigned to receive either 30 mg/day pioglitazone or a diet and exercise program for 20 weeks. Before and after the intervention, insulin sensitivity, body composition, body fat distribution (waist-to-hip ratio [WHR], computed tomography abdomen, and dual-energy X-ray absorptiometry), and abdominal and femoral fat cell size were assessed.

RESULTS: Diet and exercise resulted in an 11.8 +/- 1.1 kg weight loss. Both diet and exercise and pioglitazone improved insulin sensitivity, but only the former was associated with loss of intra-abdominal fat. Pioglitazone increased total body fat, which preferentially accumulated in the lower body depot in both men and women. WHRs decreased in both groups. Abdominal fat cell size decreased (P = 0.06) after diet and exercise. No statistically significant changes in fat cell size were observed in pioglitazone-treated volunteers.

CONCLUSIONS: In nondiabetic upper body obese subjects, increasing insulin sensitivity via diet and exercise accompanies reductions in visceral fat. Pioglitazone treatment also improves insulin sensitivity and lowers WHR, but this is due to a selective increase in lower body fat. This confirms a site-specific responsiveness of adipose tissue to TZD and suggests that improvements in insulin sensitivity by pioglitazone are achieved independent of changes in intra-abdominal fat.