Article Text


Association between physical activity and body fat percentage, with adjustment for BMI: a large cross-sectional analysis of UK Biobank
  1. Kathryn E Bradbury,
  2. Wenji Guo,
  3. Benjamin J Cairns,
  4. Miranda E G Armstrong,
  5. Timothy J Key
  1. Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, UK
  1. Correspondence to Dr Kathryn E Bradbury; kathryn.bradbury{at}


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 BMI and body fat percentage were highly correlated (r=0.85 in women; r=0.79 in men), and both were inversely associated with physical activity. Compared with <5 excess MET-hours/week at baseline, ≥100 excess MET-hours/week were associated with a 1.1 kg/m2 lower BMI (27.1 vs 28.2 kg/m2) and 2.8 percentage points lower body fat (23.4% vs 26.3%) in men, and 2.2 kg/m2 lower BMI (25.6 vs 27.7 kg/m2) and 4.0 percentage points lower body fat (33.9% vs 37.9%) in women. For a given BMI, greater physical activity was associated with lower average body fat percentage (for a BMI of 22.5–24.99 kg/m2: 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.

  • Physical activity
  • UK Biobank
  • BMI
  • Body fat percentage

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  • Contributors KEB and TJK conceived the research; KEB performed the statistical analyses; BJC contributed to the statistical methodology; MEGA contributed to generation of the physical activity variables. KEB, WG, BJC, MEGA and TJK interpreted the data, drafted and reviewed the article for important intellectual content; KEB has primary responsibility for the final content. All authors read and approved the final manuscript. KEB is the guarantor for the study

  • Funding The authors are supported by Girdlers' New Zealand Health Research Council Fellowship (KEB), Cancer Research UK (TJK; C8221/A19170 and 570/A16491), the BHF Centre of Research Excellence, Oxford (BJC; BHF no. RE/13/1/30 181), the UK Medical Research Council (MEGA and TJK; MR/M012190/1) and the Clarendon Fund and US-UK Fulbright Commission (WG). The authors had full access to all the data in the study, can take responsibility for the integrity of the data and the accuracy of the data analysis.

  • Disclaimer The funders did not influence the conduct of the study, analysis or interpretation of the data, the writing of this report or the decision to publish.

  • Competing interests All authors have completed the Unified Competing Interest form at (available on request from the corresponding author) and declare no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years, no other relationships or activities that could appear to have influenced the submitted work.

  • Patient consent Obtained.

  • Ethics approval UK Biobank has ethical approval from the North West Multi-centre Research Ethics Committee. Participants gave informed consent on the touchscreen before taking part.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement UK Biobank is an open access resource. Bona fide researchers can apply to use the UK Biobank data set by registering and applying at Statistical code used for this manuscript is available to other researchers on request by emailing Kathryn Bradbury (

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