Protein intake and nitrogen balance in male Japanese athletes

Abstract

Recommendations for the requirements for protein intake amount usually to 1.2‐2.0 g/kg BW/day in athletes. The aim of this study was to compare the effects of a high protein diet (HP: 2.5 g/kg BW/day) and a normal protein diet (NP: 1.5 g/kg BW/day) on the nitrogen balance in male Japanese athletes. Subjects were 16 healthy, male Japanese athletes (20.9±2.2 years, height: 176.2±6.3 cm, body weight: 87±14.2 kg, %fat: 17.3±6.0 %) involved in 4 different sports. These 2 regimens were further divided to HP diet or NP diet. They were participated in 2 regimens in the crossover‐randomized design during 20 days (a 7‐day adaptation period and a 3‐day balance period). Dietary intake and life activity were assessed from food and life activity records during the experimental period. To determine the effects of a HP diet, urine and blood tests were conducted and the body composition was measured. Urine samples were collected on the final three consecutive days of each diet and analyzed for nitrogen. The nitrogen balance was calculated from the mean daily protein intake, mean urinary nitrogen losses. There were no significant changes in the body composition between the HP group and the NP group. Effects of the high protein diet could not be found in the urine (24hccr, NTx, Ca, ph, oxalate) and the blood (insulin, glucose, NTx) samples. Urinary nitrogen losses increased during the HP diet vs NP diet (35.7±30.0 vs 24.0±13.7 g/kg BW/day, p<0.05). These results suggest that male Japanese athletes might not be able to efficiently incorporate a protein intake of 2.5 g/kg BW/day into their body protein. However, kind of sport; level of training; timing and amount of protein consumed at one time have not been taken into consideration and must be further analyzed.