The effect of protein intake and physical exercise on energy turnover and substrate utilisation at energy balance in man

Sammanfattning: The principal goal of the thesis has been to evaluate the effect of protein intake and physical exercise on energy turnover and substrate utilisation. Body composition assessment is of importance as an indicator of the energy balance. Therefore, in the first study the aim was to develop new models to estimate body composition more accurately. Multicompartment models were shown to improve body composition assessment as they take-into consideration individual differences in the body content of bone mineral and water. The validity of the results obtained by field-adapted methods, ie, skinfold-thickness measurement and BIA in combination, by using multicompartment instead of two-compartment equations was improved.The effect of moderate physical activity and a diet containing "high" (n=6) or "normal" (n=8) protein intake upon 24h macronutrient utilization, protein metabolism, plasma amino acid concentration and energy turnover was studied in healthy men. After a 6 day diet-exercise-adjustment period energy turnover (ET) was determined by indirect and direct (suit) calorimetry and protein turnover using [15N,15N]urea and [13C] leucine.The results showed that moderate exercise at energy balance did not affect the 24h leucine and protein balance (Paper II). They also showed that a high protein intake increased the urea production rate, the absolute rate of urea hydrolysis being unaffected (Paper III), generally decreased plasma amino acid concentration, except during feeding for branched-chain amino acids, methionine and tyrosine (Paper IV), resulted in a positive protein and carbohydrate balance and a negative fat balance compared with the normal protein intake (Paper V). These findings could be of importance for athletes interested in optimal performance, as well as of clinical significance for the dietary treatment of obesity.