Metabolic aspects of exercise and weight reduction.

Current knowledge about the thermic effects of exercise in lean and obese subjects and the relationships between exercise and food intake, resting metabolic rate, and dietary-induced thermogenesis were reviewed. Studies of the effects of carbohydrate restriction during low calorie diets on the capacity to perform physical exercise and of the effects of weight reduction with or without the addition of physical training on the metabolic abnormalities of non-insulin-dependent diabetes mellitus are also described. The metabolic efficiency of physical work is normal in obesity, total energy expenditure is increased because of increased body mass, and increased energy expenditure is not necessarily matched by a compensatory increase in caloric intake. Thus, increased physical activity can be expected to result in negative energy balance in obese subjects. It is not clear whether exercise increases resting metabolic rate, but there is considerable evidence that exercise may potentiate the thermic effect of food in lean subjects and that this response may be blunted in the obese. The capacity to perform moderate-intensity exercise during carbohydrate-restricted, low calorie diets is maintained after a period of adaptation, but the capacity for high-intensity exercise (greater than 70% VO2max) is decreased unless adequate carbohydrate is provided to maintain muscle glycogen stores. The major effect of the addition of a program of physical training to dietary restriction and weight reduction in the treatment of non-insulin-dependent diabetes mellitus is an increase in peripheral sensitivity to insulin, primarily due to increased non-oxidative glucose disposal in muscle tissue.