Associations between physical activity and fat mass in adolescents: the Stockholm Weight Development Study

Background: Obesity is multifactorial. However, the accumulation of fat mass (FM) is proposed to be due to a positive energy balance, which may be caused by reduced physical activity (PA). Objective: The objectives of the study were to describe the independent associations between PA and FM in adolescents and to describe the intergenerational association of FM between mothers and their offspring. Design: We conducted a cross-sectional study in 445 (190 M, 255 F) 17-y-old adolescents and their mothers. PA was assessed with a self-reported questionnaire and validated by comparison with accelerometric data in a subsample of the cohort. Body composition was measured by using air-displacement plethysmography. Results: Males were significantly more active than were females (P < 0.01). PA was significantly and inversely associated with FM (beta = -3.63, P = 0.005) and percentage FM (beta = -3.117, P = 0.017) in males but not in females (beta = -0.576, P = 0.54; beta = -0.532, P = 0.59, respectively) after adjustment for birth weight and maternal FM and education level. However, FM and percentage FM in females were significantly associated with maternal FM (beta = 0.159, P < 0.0001; beta = 0.145, P = 0.002, respectively) and education level (beta = -1.048, P < 0.005; beta = -1.085, P = 0.006, respectively). No such associations were observed in males. Conclusions: PA was independently associated with FM in males but not in females. The data also showed an intergenerational association of FM between mothers and their daughters but not between mothers and their sons.