The impact of food intake and exercise on energy expenditure.

Food intake and physical exercise affect two components of energy expenditure, resting metabolic rate (RMR) and the thermic effect of feeding (TEF). Classic studies of overfeeding and underfeeding clearly showed that caloric deficit and surfeit conditions alter RMR. Recent work on short-term overfeeding of monozygotic twins provides new evidence that genetic factors influence individual sensitivity to changes in RMR and TEF when caloric excess is present. Exercise affects energy expenditure during nonactive times; acute bouts of vigorous exercise may result in increased RMR, and this effect appears most pronounced in the first 12 h after exercise. Acute exercise may potentiate the thermic effects of food when they are taken together, and high levels of exercise training may increase RMR. Thus, physical exercise appears to play an important role in the regulation of energy balance by way of its direct energy cost and its influence on RMR and TEF.