A paper in the International Journal of Epidemiology seeks to dismiss the concept of 'fat but fit' and instead suggest that the protective effects of high fitness against early death are reduced in obese people as it appears obesity is far more dangerous than a lack of physical fitness.
Researchers at Umeå University in Sweden sought to find whether the negative health effects of obesity could be canceled out by increasing fitness levels, based on both being associated with death at older ages.
The study analyzed data on 1.3 million Swedish men followed from 1969 to 1996, with aerobic fitness measured by an electrically braked cycle test and causes of death tracked using Swedish national registers.
What they found is that the risk of early death is much lower in normal-weight men at all fitness levels than men who are obese but aerobically fit. Even in those normal-weight men who registered at the bottom of the fitness scale, the risk was 30 percent lower than those who consider themselves "fat but fit."
On the other hand, obese people still benefit from exercise but the findings of the study suggest that the benefits weaken the more obese a person is when it comes to reducing risk of death. The study was limited to men and so researchers cannot rule out that "fat but fit" doesn't apply to women or not.