Contestants from "The Biggest Loser," episode 801 (NBC Photo: Dave Bjerke)

One of the most controversial ideas in medical science today is whether people can really be fat and fit. That is, is weight in itself a marker of health -- or simply a suggestion of a person's physical fitness?

A key study in this debate was published in 2012 by a team of researchers from the United States and Europe in the European Heart Journal. They argued that overweight and obese people were at no greater risk of heart disease or cancer as compared with those of normal weight -- as long as they were "metabolically fit."

By that they meant not having insulin resistance, diabetes, high triglycerides or high blood pressure and having good cholesterol levels. An astounding percentage -- nearly half  of the 43,000 obese people they had data on -- were deemed fit according to this criteria, and when compared against similarly healthy normal weight participants, the fit obese participants had no higher risk of death.

That settled the issue for many, but a large new study out this week in the International Journal of Epidemiology adds another dimension to our knowledge about how weight affects our health by focusing specifically on aerobic fitness.

The analysis involved data from 1,317,713 men in Sweden for an average of 29 years. Researchers evaluated their aerobic fitness by asking them to cycle until they got tired.

Men who weighed in in the normal range, regardless of their fitness level, appeared to have a lower risk of death as compared to those who were obese but fit (in the highest quarter of aerobic fitness).  Even more striking: the beneficial effect of high aerobic fitness appeared to be reduced with increased obesity. In fact, those at the most extreme in terms of obesity did not see a benefit at all from aerobic fitness.

The researchers said the findings suggests that being obese may reduce the protective effects of being fit. "This data does not support the notion that 'fat but fit' is a benign condition," they wrote.

Of course this study is limited because it only involved men and the researchers noted that many in their sample died relatively early. Other recent research has highlighted the idea that it isn't just your weight that impacts your health risks, but where it is on your body (like your mid-section or belly).

In fact, as one researcher told The Washington Post as far back as 2004, "this is something that really shouldn't be a debate of one versus the other."

"It's clear that both fitness and fatness are important," said Walter Willett, an expert on nutrition and health at the Harvard School of Public Health. "It's definitely good to be as fit as possible no matter what your body weight. But it's also clear that it is optimum to be both lean and fit. It shouldn't be a question of one or the other."

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