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±â0.8% CHO, 60.4%â±â0.3% fat, and 15.5%â±â1.0% protein), CHO-rich (69.3%â±â1.2% CHO, 15.9%â±â2.1% fat, and 15.1%â±â1.1% protein), or habitual (56.1%â±â7.0% CHO, 27.5%â±â4.9% fat, and 16.5%â±â4.0% protein) diet, 19 trained adolescent boys (15.2â±â1.5 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 (Pâ<â0.05), 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 (50.0â±â7.0, 51.9â±â8.3, and 50.9â±â7.4âminutes, respectively), but consuming a CHO-rich diet enhanced performance compared with that after a fat-rich diet (Pâ=â0.03). 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.
