Associations between muscle mass, physical activity and dietary behaviour in adolescents.

BACKGROUND AND OBJECTIVES: Investigations in older individuals suggest that adequate nutrition and physical activity are particularly important to skeletal muscle health; however, data in adolescents are scant and equivocal. The objective was to determine the associations among diet, physical activity and skeletal muscle mass in adolescents. METHODS: We assessed diet with four to seven 24-h recalls and physical activity by accelerometry in 640 adolescents. Using total body measures of fat-free soft tissue mass and fat mass assessed by dual-energy X-ray absorptiometry, the skeletal muscle mass index (SMMI) was derived by adjusting fat-free soft tissue mass for fat mass in addition to height. RESULTS: Skeletal muscle mass index (SMMI) was negatively associated with consumption of sugar-sweetened beverages (standardized beta coefficient [ß] = -0.10, P = 0.001) and saturated fats (ß = -0.28, P < 0.001). SMMI was positively associated with physical activity (moderate + vigorous) (ß = 0.20, P < 0.001). In further analysis, we observed a significant interaction between physical activity and sugar-sweetened beverage intake on SMMI (P = 0.002). CONCLUSION: Our study in adolescence suggests that physical activity and consumption of both sugar-sweetened beverages and saturated fats are associated with skeletal muscle mass. More importantly, our findings suggest that sugar-sweetened beverage intake may attenuate the beneficial effects of physical activity on skeletal muscle mass.