A large study of more than 1.3 million men in Sweden has challenged the claim that obesity is not a health risk if the individual is fit. In this case, the authors focussed on aerobic fitness by asking young men (mean age, 18 years) to cycle until they had to stop due to fatigue and then following them up over the long term.
Over a mean follow-up of 29 years, 44 301 participants died (3.36%). Overall, men in the highest quintile of fitness were at substantially lower risk of dying than those in the lowest quintile (hazard ratio [HR], 0.49; 95% confidence interval [CI], 0.47–0.51). Similar risks were found for weight-adjusted aerobic fitness. However, while aerobic fitness was associated with a reduced risk of death in normal-weight and overweight men (according to BMI), obese men saw no benefit (P<0.001 for interaction). Furthermore, unfit men who were of normal weight had a 30% lower all-cause mortality risk than men in the top fitness quintile who were obese (HR, 0.70; 95% CI, 0.53–0.92).
This study is of course limited by the entirely male cohort, and the authors note that there was a surprisingly high rate of early death, including deaths related to alcohol, drugs and trauma; however, the findings suggest that aerobic fitness cannot fully counteract the effects of obesity on health.
The study can be read in the International Journal of Epidemiology here.
