Dependence of 24 h energy expenditure in man on the composition of the nutrient intake.

The influence of the nutrient composition of food on energy expenditure during a 24 h period was investigated in adult volunteers. The maximum probable effect was determined using iso-energetic diets high in either protein or in glucose. Two men and four women took part in the study. Their body-weights and body composition were within the normal range. Each subject lived for 28 h in a whole-body calorimeter set at 26 degrees, on two separate occasions. During each session they ate one of the following iso-energetic diets: high-protein-low-carbohydrate or high-glucose-low-protein. Energy expenditure was determined while the subject followed a pre-set pattern of activity. A 24 h collection of urine was made and total nitrogen, creatinine and urea excretions were determined, so that heat production could be corrected for protein metabolism. Two independent measures of energy expenditure were made: direct calorimetry was used to obtain heat loss partitioned into its sensible and evaporative components, while indirect calorimetry was used to estimate heat production from oxygen consumption, carbon dioxide production and N excretion. There was good agreement between the two estimates of 24 h energy expenditure: for the twelve sessions in the calorimeter the mean difference between heat production and heat loss was only 0.4 (SEM 0.39)%. The results showed that nutrient composition can have a marked influence on 24 h energy expenditure in adult humans. Mean values of 8659 (SEM 230) kJ and 7735 (SEM 250) kJ were obtained for the high-protein and high-glucose diets respectively. This 12% increase in energy expenditure on the high-protein intake was significant (P less than 0.001). On the high-glucose intake, total heat loss comprised 22 and 78% evaporative and sensible heat losses respectively. The increase in heat loss on the high-protein intake was accounted for by a 39% increase in evaporative heat loss and a 7% increase in sensible heat loss. It is concluded that the composition of the nutrient intake has a greater influence on the metabolic rate of adult humans than has been suggested by some groups of workers in recent years.