Do you believe that there is such a thing as being "fat but fit"? Well, a surprising new study might have you thinking otherwise.

The study found that while body size is not necessarily an indication of fitness — that is, you can be obese and still perform better aerobically than a slim person — body size is still a more predictive measure of overall health than fitness. In other words, being fat but fit is still less healthy than being thin and lazy, reports Science Daily.

Swedish researchers followed 1,317,713 men for a median average of 29 years in an effort to examine the association between aerobic fitness and death later in life. Subjects were categorized by their body type (measured in Body Mass Index), and their aerobic fitness was tested by asking them to cycle until they had to stop due to fatigue.

Incredibly, the research indicated that obese people with high levels of aerobic fitness were still 30 percent more likely to die prematurely even when compared with those who were slim but did little exercise. To put it plainly, fitness cannot make up for being overweight when it comes to your overall life expectancy.

The study also found that the beneficial effect of high aerobic fitness was reduced with increased obesity, and in those with extreme obesity there was no significant effect at all. In other words, fitness had an increasingly reduced impact on health the more obese a person was.

It's important to understand that these results, though surprising, are not an excuse to give up on exercise. Being slim but unfit was still less healthy than being slim and fit. Likewise, obese fit people were still better off than obese unfit people overall. And of course, aerobic fitness is an important tool that obese people can use as part of an effort to transform their bodies and lose weight.

Having said that, the idea that it is okay to be fat if you're fit appears to have been proven incorrect, at least according to how this study drew its measurements.

It should be noted that the study, though rather large and comprehensive, only looked at men. So it's unclear if these same results would apply to women. The study also only measured health in terms of life expectancy and the risk of early death. It's therefore possible that obesity is correlated with risk of death for reasons other than health. For instance, obese people may tend to possess linked genetic predispositions to conditions that cause early death that simply have nothing to do with fitness at all, thus clouding the study's conclusions. This alternative is mere speculation, however.

Either way, the study is an eye-opener and could rewrite the book of how we think about health and fitness on the whole. It further emphasizes just how dangerous being overweight can be.