Effects of excessive caloric intake and caloric restriction on body weight and energy expenditure at rest and light exercise

The individual response to overeating and semistarvation on energy expenditure at rest and light work before and after a test meal was investigated. This response was related to the change in dry body weight, measured as weight (W) minus total body water (TBW). Experiments were performed on 9 non-obese subjects: (a) with a normal habitual energy intake; (b) (overfeeding) with an extra energy intake of 12 MJ per day for two weeks; and (c) (semistarving) with an energy intake of only 2.1 MJ per day for 2 weeks. Measurements of VO₂, VCO₂. W and TBW were obtained at the end of each of the three periods. It was found that the perturbation in energy intake from normal to 20–25 MJ per day increased the energy expenditure. The magnitude of this increase was highly individual and inversely related to the change in dry body weight. Energy expenditure, measured under the four standardized conditions, after 2 weeks of semistarvation was lower than that obtained after the preceding overeating period. This decrease was also roughly inversely related to the change in dry body weight. The results support the idea that part of the regulation of body energy content takes place by way of a change in the efficiency of energy utilization and that the response to a perturbed energy intake varies considerably between subjects.