501. Epidemiology and Biostatistics - epidemiology of physical activity and health Scientific Abstract

2051 - All-cause Mortality And The Fat-but-fit Hypothesis: A Reexamination Using Uk Biobank

Session Type
Rapid Fire Platform
Session Name
D-47 - New Findings in Physical Activity and Health
Session Category Text
Physical Activity/Health Promotion Interventions
Disclosures
 J. Tarp: None.

Abstract

Obesity is associated with an increased risk of premature mortality, but observational studies implies that obese adult with high cardiorespiratory fitness (CRF; ‘fat-but-fit’) may not be at an increased risk. However, the evidence for the ‘fat-but-fit’ hypothesis is limited by insufficient control of confounding from smoking and risk of reverse-causality bias from pre-existing conditions.
PURPOSE: To examine evidence for the ‘fat-but-fit’ hypothesis using different approaches for reducing confounding and reverse-causality bias.
METHODS: CRF was estimated from linear extrapolation of the heart rate response during a submaximal bicycle ergometer test in women and men from the UK Biobank cohort. Watts per kg fat-free mass was split into unfit (<20%) or fit (>60%) based on the age-sex stratified sample distribution and combined with measured body-mass index (BMI) as normal weight (NW; BMI 18.5 – 25) or obese (BMI ≥ 30) yielding four CRF-BMI combinations. All-cause mortality was ascertained from death registers. Multivariable-adjusted cox-regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI).
RESULTS: Over a median follow-up of 7.7 years, 580 deaths in 26,315 participants were recorded. In analysis adjusting for prevalent CVD/cancer and using NW-fit as the reference, being NW-unfit or obese-unfit were associated with increased mortality with HRs of 1.45 (CI: 1.15, 1.83) and 1.64 (1.29, 2.09), see figure. Mortality was not increased in the obese-fit against the reference (1.16 (CI: 0.92, 1.47). Associations were attenuated when excluding individuals with prevalent CVD/cancer and early deaths. Re-analyzing with restriction to never-smokers resulted in similar HRs across the fat-fit combinations against the NW-fit reference.
CONCLUSION: Obese-unfit, but not obese-fit, individuals have an increased risk of premature mortality as compared with NW-fit individuals. The association appears susceptible to bias.
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