This study of 14,345 men found that maintaining or increasing physical fitness played a more important role in reducing the risk of mortality than changes in BMI.

At the start of the study, and periodically for the next 6.3 years, the men underwent maximal treadmill tests and had their BMI measured. Changes between the baseline and last examination were used to classify the men as losing fitness or BMI, having stable fitness or BMI, or gaining fitness or BMI.

During the 11.4-years after the last exam there were 914 all-cause deaths and 300 cardiovascular (CVD) deaths. After controlling for changes in BMI, stable fitness was associated with 30% lower odds of all-cause mortality and 27% lower odds of CVD mortality, than losing fitness.

Increasing fitness was associated with 39% lower risk of all-cause mortality and 42% lower odds of CVD mortality. Each 1 MET improvement in fitness was associated with a 15% reduction in the odds of all-cause death and 19% lower odds of CVD death.

After adjusting for changes in fitness, changes in BMI were not associated with mortality risks. In an analysis that combined changes in fitness and BMI, men who lost fitness had higher odds of dying regardless of changes in their BMI.

“This is good news for people who are physically active but can’t seem to lose weight,” says lead researcher Duck-chul Lee, Ph.D. “You can worry less about your weight as long as you continue to maintain or increase your fitness levels.”