Energy metabolism inresponse 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 2 219 kcal/d) and the subjects lost 0.8 -t 0.3 kg body weight. During the 8-day hypercaloric diet period, TDEE increased by 425 f 103 kcal/d (P = .03), which dissipated 25% 5 5% of the increased energy intake. One fourth of the increase in TDEE was caused by an increase in RMR (110 2 24 kcal/d, P = .02) and the remainder by an increase in NREE (316 2 103 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. Copyright c 1993 by W. B. Saunders Company B ODY WEIGHT STABILITY over long periods of time reflects an extraordinary relationship between energy intake and energy expenditure. Most adult humans in Western civilizations ingest approximately 900,000 kcal/yr without large changes in body weight.’ Even small differcncss in daily energy balance over long periods of time could have dramatic effects on body weight. For example, ingesting only 25 kcal/d more than expended, a 1% error in energy balance, would theoretically cause an accumulation ot‘ about 1 kg body fat in 1 year. Therefore, it is remarkable that without conscious effort most persons match energy intake so closely with energy expenditure and can maintain a constant weight. The effect of overfeeding on energy metabolism has important public health and clinical implications because the accumulation of fat in obese persons is caused by long-term excessive caloric intake. It has been proposed that energy expenditure increases during overfeeding because weight gain has often been found to be less than that theoretically predicted by the amount of excess calories ingested.‘-” However, studies that have actually measured total energy expenditure during overfeeding have been confusing because of conflicting results. Total energy expenditure has been reported to decrease,h remain the same,‘J or incrcase”-lz after increasing caloric intake. In evaluating the adaptative response of energy metabolism to overfeeding, it is important to take into account the various components of total daily energy expenditure (TDEE)-resting metabolic rate (RMR), thermic effect of food (TEF), and thermic effect of physical activity (TEPA).‘? Most studies have reported a small increase in RMR after overfceding.h,‘l,‘T-lJ The absolute TEF is also increased because TEF is a direct function of the amount of calories ingested.” The effect of overfeeding on physical activity is difficult to examine because of practical limitations in its measurement. The daily energy costs associated with physical activity include the energy cost required for the activities of daily living, exercise, spontaneous physical activity. and fidgeting. Energy expended by physical activity should increase during overfeeding if body mass increases and activity is maintained.‘” It seems logical that TDEE would increase during