A study published in the International Journal of Epidemiology challenged the concept that by being physically fit, individuals who are obese can fully compensate mortality risk. The study suggested that physically fit obese men have a higher risk for death compared to men who are of normal weight but are physically unfit. And it also found a graded association between aerobic fitness at the age of 18 years and the risk of early death.

The study by Gabriel Högström, Dept. of Community Medicine and Rehabilitation at Umeå University, Sweden, and colleagues, obtained data from the Swedish Military Conscription Registry and included 1,317,713 Swedish men (mean age, 18 years) conscripted into the Swedish military from 1969 to 1996. At the time of conscription, they were subjected to baseline assessments for aerobic fitness testing, wherein they cycled until fatigue set in. Investigators assessed all-cause and cause-specific deaths, using national registers. Mortality information was obtained from the National Cause of Death Registry.

Over a mean follow-up of 28.8 years, 44,301 of them died. After adjustment for age and conscription year, those with the highest aerobic fitness levels were found to have a 51% lower risk for all-cause death compared to those with the lowest fitness levels. Similar findings were seen from analyses of weight-adjusted fitness.

Alcohol and narcotic abuse were found to have the strongest associations with death (HR, 0.20; 95% CI, 0.15 – 0.26).

Obese men obtained lesser benefit than normal-weight men from being physically fit (P < .001). Additionally, normal-weight men in all levels of aerobic fitness had lower risk for all-cause mortality (30% – 48%; P < .05 for all) in comparison with obese men with the highest levels of aerobic fitness.

The benefits of aerobic fitness appeared to decline with increase in weight. After adjusting for age and year, normal-weight men in the upper half of aerobic fitness had 34% lower risk for death compared to those in the lower half (HR, 0.66; 95% CI, 0.64 – 0.68). The benefit was seen to decrease to 28% among overweight men, and disappeared completely in those with the highest levels of obesity… (Medscape)