The effects of a 10-day low-calorie diet (LCD; n = 8) or exercise training (ET; n = 8) on insulin secretion and action were compared in obese men (n = 9) and women (n = 7), aged 53 ± 1 yr, with abnormal glucose tolerance by using a hyperglycemic clamp with superimposed arginine infusion and a high-fat drink. Body mass (LCD, 115 ± 5 vs. 110 ± 5 kg; ET, 111 ± 7 vs. 109 ± 7 kg; P < 0.01) and fasting plasma glucose (LCD, 115 ± 10 vs. 99 ± 4 mg/dl; ET, 112 ± 4 vs. 101 ± 5 mg/dl, P < 0.01) and insulin (LCD, 23.9 ± 5.6 vs. 15.2 ± 3.9 µU/ml; ET, 17.6 ± 1.9 vs. 13.9 ± 2.4 µU/ml; P < 0.05) decreased in both groups. There was a 40% reduction in plasma insulin during hyperglycemia (0-45 min) after LCD (peak: 118 ± 18 vs. 71 ± 14 µU/ml; P < 0.05) and ET (69 ± 14 vs. 41 ± 7 µU/ml; P < 0.05) and trends for reductions during arginine infusion and a high-fat drink. The 56% increase in glucose uptake after ET (4.95 ± 0.90 vs. 7.74 ± 0.82 mg · min¹ · kg fat-free mass¹; P < 0.01) was significantly (P < 0.01) greater than the 19% increase (5.72 ± 1.12 vs. 6.80 ± 0.94 mg · min¹ · kg fat-free mass¹; P = not significant) that occurred after LCD. The marked increase in glucose disposal after ET, despite lower insulin levels, suggests that short-term exercise is more effective than diet in enhancing insulin action in individuals with abnormal glucose tolerance.

hyperglycemic clamp; low-calorie diet; exercise training; glucose disposal

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