Energy metabolism in response to overfeeding in young adult men

The effect of overfeeding on energy metabolism was evaluated in four young adult men of normal weight. Subjects were fed a hypocaloric diet for 8 days followed by an 8-day hypercaloric diet to maximize differences in the metabolic response to the two diets. Energy intake during the hypocaloric and hypercaloric phases was 1.32 and 2.26 times resting metabolic rate (RMR), respectively. Additional calories during hypercaloric feeding were provided as 1,659 +/- 40 kcal/d carbohydrate and lipid. Total daily energy expenditure (TDEE) was measured by the doubly labeled water technique and RMR by indirect calorimetry. Nonresting energy expenditure (NREE) was calculated as the difference between TDEE and RMR. During the 8-day hypocaloric diet period, energy intake was approximately 340 kcal/d less than the measured rate of TDEE (2,384 +/- 219 kcal/d) and the subjects lost 0.8 +/- 0.3 kg body weight. During the 8-day hypercaloric diet period, TDEE increased by 425 +/- 103 kcal/d (P = .03), which dissipated 25% +/- 5% of the increased energy intake. One fourth of the increase in TDEE was caused by an increase in RMR (110 +/- 24 kcal/d, P = .02) and the remainder by an increase in NREE (316 +/- 103 kcal/d, P = .05). These results demonstrate that only a small portion of excess energy intake is dissipated by an increase in energy expenditure. NREE can be an important component of the increase in energy metabolism during overfeeding.