Effect of fat- and carbohydrate-rich diets on metabolism and running performance in trained adolescent boys.

ABSTRACT

OBJECTIVES: A randomized crossover trial was designed to analyze the impact of a short-term, isoenergetic fat-rich or carbohydrate (CHO)-rich diet on substrate oxidation rates during submaximal exercise and on performance in a 10,000-m running time trial in trained, mid- to late-pubertal boys. METHODS: An incremental test was performed to determine the peak oxygen uptake (VO2peak). After 2 days on a fat-rich (24.2% ±â€Š0.8% CHO, 60.4% ±â€Š0.3% fat, and 15.5% ±â€Š1.0% protein), CHO-rich (69.3% ±â€Š1.2% CHO, 15.9% ±â€Š2.1% fat, and 15.1% ±â€Š1.1% protein), or habitual (56.1% ±â€Š7.0% CHO, 27.5% ±â€Š4.9% fat, and 16.5% ±â€Š4.0% protein) diet, 19 trained adolescent boys (15.2 ±â€Š1.5 years) performed a 10-minute constant run at 65% VO2peak to determine the respiratory exchange ratio (RER) during exercise and 10,000-m running on an outdoor track. RESULTS: During the constant run, the RER and CHO contribution to energy expenditure were lower, and fat contribution higher, in the fat-rich diet than in the CHO-rich diet (P < 0.05), but the results were not different from those of the habitual diet. Performance in the 10,000-m run after consuming CHO- and fat-rich diets was similar to performance after a habitual diet (50.0 ±â€Š7.0, 51.9 ±â€Š8.3, and 50.9 ±â€Š7.4 minutes, respectively), but consuming a CHO-rich diet enhanced performance compared with that after a fat-rich diet (P = 0.03). CONCLUSIONS: These findings indicate that a CHO-rich diet provides additional benefits to 10,000-m running performance in trained adolescent boys compared with a fat-rich diet.