Protein Needs in Adolescent Sprint Athletes: a Longitudinal Study

Abstract

Nutrition plays a key role in health, performance, growth and development, especially in adolescent athletes. Adequate protein intake is important for optimal lean tissue repair and acquisition. Nitrogen balance studies are usually used to determine the specific protein needs for different types of athletes. Data regarding protein intake recommendations for adolescent sprint athletes are scarce. PURPOSE: To estimate protein needs for sprint athletes during adolescence. METHODS: A 7-day diet diary, during which period 2 × 24hour urine samples were collected, was administered 5 times with a 6 month interval to 32 female and 33 male adolescent sprint athletes (age at start respectively 14.8±1.6 and 14.7±1.9yrs). Anthropometric data were collected allowing the estimation of skeletal muscle mass (SMM). Diaries were analyzed for nutrient intakes using the Belgian and Dutch food data banks. A cut-off value of 1.1 x basal metabolic rate was used to check for underreporting. During the 24hour urine collections, athletes ingested 3 x 180mg para-amino benzoate. Urine collections containing a minimum of 85% para-amino benzoate were analyzed for their nitrogen content using the Kjeldahl method. All data were normally distributed. ANOVA procedures and Pearson correlations were applied at the 5% confidence level. RESULTS: Mean daily protein intakes remained within a narrow range of 1.4±0.3 and 1.5±0.3g/kg in girls (p=.49) and 1.5±0.3 and 1.6±0.3g/kg in boys (p=.15). For both genders, a protein intake around 1.4g/kg was required to be in a positive nitrogen balance. This remained stable throughout the experimental period. Girls became 2.8±3.6cm taller, 4.7±3.0kg heavier and acquired 1.6±1.7kg SMM between the 1st and 5th measurement. Boys gained 5.5±6.0cm in height, 8.0±4.6kg in weight and 3.6±2.3kg in SMM. Height and weight evolution was comparable to that of their Belgian peers. A gain in body height, weight or SMM did not alter nitrogen balance in both genders. There was no significant relation between protein intake and a gain in height, weight or SMM. CONCLUSIONS: A daily protein intake between 1.3-1.5g/kg appears adequate to sustain a positive nitrogen balance in sprint adolescent male and female athletes. Sufficient protein was provided through the diet in most of the athletes studied.