Short-term weight loss and exercise training effects on glucose-induced thermogenesis in obese adolescent males during hypocaloric feeding.

Our purpose was to examine the effect of short-term weight loss and exercise training on the thermic effect of a glucose load in lean and obese adolescents. Nine obese (age 14.3 +/- 0.3 years, mean +/- s.e.m.) boys were examined during the first (Ob-pre) and sixth (Ob-post) week of caloric restriction (1300-1500 kcal/day, 5441-6279 kJ/day) and aerobic exercise conditioning (walk/jog/swim/calisthenics), and compared to age-matched lean controls (Con). A 100-g oral glucose tolerance test (OGTT) was administered while simultaneously measuring energy expenditure by indirect calorimetry every 30 min for 3 h. Posttest results revealed a decrease in body weight and body fatness in obese boys, but not to the level of that in lean controls (P less than 0.01). The thermic effect of glucose, calculated as the area under the response curve for three hours in excess of resting metabolic rate, was similar in Ob-pre and Con (0.77 +/- 0.14 vs. 0.57 +/- 0.28 kcal/kg lbm/3h), but decreased in Ob-post (0.29 +/- 0.08 kcal/kg lbm/3h, P less than 0.01). The area under the response curve for glucose was elevated in Ob-pre (328.1 +/- 12.2 mg/dl/3h) compared to Con (270.4 +/- 21.4 mg/dl/3h). The insulin response was similar in Ob-pre and Con (120.4 +/- 11.3 vs 125.6 +/- 12.4 mU/ml/3h), but decreased in Ob-post (89.6 +/- 15.1 mU/ml/3h, P less than 0.05). Thus, the improvement in peripheral insulin sensitivity with short-term exercise and weight loss was unaccompanied by favorable alterations in carbohydrate-induced thermogenesis in obese adolescents.