PROTEIN-TURNOVER AND THERMOGENESIS IN RESPONSE TO HIGH-PROTEIN AND HIGH-CARBOHYDRATE FEEDING IN MEN

The rates of energy expenditure and whole-body protein turnover were determined during a 9-h period in a group of seven men while they received hourly isocaloric meals of high-protein (HP) or high-carbohydrate (HC) content. Their responses to feeding were compared with those to a short period of fasting (15-24 h). The 9-h thermic response to the repeated feeding of HP meals was found to be greater than that to the HC meals (9.6 ± 0.6% vs 5.7 ± 0.4% of the energy intake, respectively, x̄ ± SEM,p < 0.01 ). The rate of whole-body nitrogen turnover over 9 h increased from 17.6 ± 2.2 g on the fasting day to 27.4 ± 1.4 g during HC feeding (NS) and there was a further increase to 58.2 ± 5.3 g resulting from HP feeding (p < 0.001). By using theoretical estimates (based upon ATP requirements) of the metabolic cost of protein synthesis, 36 ± 9% of the thermic response to HC feeding and 68 ± 3% of the response to HP feeding could be accounted for by the increases in protein synthesis compared with the fasting state.