Association between physical activity and body fat percentage, with adjustment for BMI: a large cross-sectional analysis of UK Biobank

OBJECTIVES: The objective of this study was to examine if, in the general population, physically active adults have less body fat after taking body mass index (BMI) into account. DESIGN: A cross-sectional analysis of participants recruited into UK Biobank in 2006-2010. SETTING: UK Biobank assessment centres throughout the UK. PARTICIPANTS: 119 230 men and 140 578 women aged 40-69 years, with complete physical activity information, and without a self-reported long-term illness, disability or infirmity. EXPOSURES: Physical activity measured as excess metabolic equivalent (MET)-hours per week, estimated from a combination of walking, and moderate and vigorous physical activity. BMI from measured height and weight. MAIN OUTCOME MEASURE: Body fat percentage estimated from bioimpedance. RESULTS: : 2.0 (95% CI 1.8 to 2.2), percentage points lower body fat in men and 1.8 (95% CI 1.6 to 2.0) percentage points lower body fat in women, comparing ≥100 excess MET-hours per week with <5 excess MET-hours/week). CONCLUSIONS: In this sample of middle-aged adults, drawn from the general population, physical activity was inversely associated with BMI and body fat percentage. For people with the same BMI, those who were more active had a lower body fat percentage.