Abstract
Aging is associated with an increased accumulation of abdominal fat, glucose intolerance, and insulin resistance. We tested the hypothesis that diet-induced weight loss would reduce the abdominal distribution of fat and improve glucose tolerance and insulin action in a group of obese middle-aged and older men with normal or impaired glucose tolerance (IGT). Oral glucose tolerance tests (OGTTs) were performed at baseline and after 9 months of diet-induced weight loss in 35 men (mean age, 60 ± 8 years). Fifteen men of comparable age and degree of obesity who did not participate in the weight loss intervention served as controls. Subjects lost 9.0 ± 2.0 kg (mean ± SD) body weight ( P < .001), resulting in a 19% reduction in percent body fat (30.0 ± 4.0% to 24.0% ± 4.0%, P < .001), an 8% reduction in waist circumference (104.0 ± 7.0 to 96.0 ± 7.0 cm, P < .001), and a 2% reduction in waist to hip ratio [WHR] (0.97 ± 0.06 to 0.95 ± 0.06, P < .01). Weight loss improved glucose tolerance: nine men with IGT at baseline reverted to normal glucose tolerance following the intervention. Glucose area during the OGTT was significantly reduced after weight loss (−22.0%, P < .001), while it increased in control subjects (+32%, P < .004). In multiple regression analysis, the improvement in glucose area following weight loss in these 35 men was attributed to the reduction in waist circumference ( P < .01) and baseline glucose area ( P < .05). Insulin response to glucose and tissue sensitivity to endogenous insulin were measured in a subset of eight men using the hyperglycemic clamp technique. Weight loss resulted in significant reductions in acute ( P < .05) and second-phase ( P < .01) insulin responses and a significant increase in the rate of glucose utilization ([M] P < .05), indicative of increased tissue sensitivity to insulin. Our results support the hypothesis that weight loss significantly improves glucose tolerance and insulin action in obese middle-aged and older men with normal glucose tolerance or IGT, in part by reducing the distribution of fat in upper-body sites.
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