POSTPRANDIAL THERMOGENESIS AT REST AND POSTEXERCISE BEFORE AND AFTER PHYSICAL-TRAINING IN LEAN, OBESE, AND MILDLY DIABETIC MEN

To determine the independent impact of physical training on postprandial thermogenesis at rest and after 1 hour of cycling at 100 W, 10 lean (15% ± 1% body fat), 10 obese (33% ± 2% fat), and six obese diet-controlled, type II diabetic men (34% ± 4% fat) underwent 12 weeks of vigorous cycle ergometer training (4 h/wk at ∼70% of maximum oxygen consumption [VO2max]) while maintaining body weight and composition. Body weight was held constant by refeeding the energy expended in each training session. Cardiorespiratory fitness increased by approximately 27%, but body weight and fat did not change. Before and at least 4 days after the last exercise session, energy expenditure was measured for 3 hours under four conditions: (1) rest, no meal; (2) rest, after a 720-kcal mixed meal; (3) postexercise after 1 hour cycling, no meal; and (4) postexercise, meal after exercise. The thermic effect of food was calculated as postprandial minus postabsorptive energy expenditure at rest and postexercise (kcal/3 h). Before and after training, the thermic effect of food during rest was lower in obese than in lean men, and lower in diabetic than in obese men (P < .05). Thermogenesis was improved after short-term exercise in obese and diabetic men compared with that at rest, but was not normalized (P < .05 for lean v obese, diabetic men). A significant effect of training on thermogenesis was due to a small but significant increase after training for diabetic men under the postexercise condition. Thus, while short-term exercise enhances but does not normalize thermogenesis in obese and diabetic men, long-term exercise training leading to increased cardiorespiratory fitness, in the absence of changes in body composition, leads to a small increase in thermogenesis in diabetic men, which manifests only after a short period of exercise. © 1992.