Oxford University Press
A new study, published today in theInternational Journal of Epidemiology [1], has dismissed the concept of 'fat but fit'. In contrast, the results from the new study suggest that the protective effects of high fitness against early death are reduced in obese people.
Although the detrimental effects of
low aerobic fitness have been well documented, this research has largely been
performed in older populations. Few studies have investigated the direct link
between aerobic fitness and health in younger populations.
This study by academics in Sweden followed 1,317,713 men for a median average of 29 years to examine the association between aerobic fitness and death later in life, as well as how obesity affected these results. The subjects' aerobic fitness was tested by asking them to cycle until they had to stop due to fatigue.
Men in the highest fifth of aerobic
fitness had a 48 per cent lower risk of death from any cause compared with
those in the lowest fifth. Stronger associations were observed for deaths
related to suicide and abuse of alcohol and narcotics.
Unexpectedly, the
authors noted a strong association between low aerobic fitness and also deaths related
to trauma. Co-author Peter Nordström has no explanation for this finding:
"We could only speculate, but genetic factors could have influenced these
associations given that aerobic fitness is under strong genetic control."
The study also evaluated the concept
that 'fat but fit is ok'. Men of a normal weight, regardless of their fitness
level, were at lower risk of death compared to obese individuals in the highest
quarter of aerobic fitness.
Nevertheless, the relative benefits of high fitness
may still be greater in obese people. However, in this study the beneficial
effect of high aerobic fitness was actually reduced with increased obesity, and
in those with extreme obesity there was no significant effect at all.
With the limitation that the study cohort
included only men, and relative early deaths, this data does not support the
notion that 'fat but fit' is a benign condition.