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

A new study shows that even with healthy blood pressure, blood sugar and cholesterol levels, an overweight or obese person has a higher risk of heart disease than someone who is not overweight.

Researchers from the Imperial College London and the University of Cambridge examined the medical records of nearly half a million people. They took into account body mass index (BMI) and whether people were healthy or unhealthy — defined by whether they had three or more metabolic markers like high blood pressure, high blood sugar, low levels of HDL cholesterol or a high waist circumference.

The study found that compared to the healthy-weight control group, people marked as unhealthy had more than double the risk of heart disease, regardless of weight. But overweight and obese people who were deemed "healthy" by their metabolic markers still carried a higher risk for heart attacks.

“Our findings suggest that if a patient is overweight or obese, all efforts should be made to help them get back to a healthy weight, regardless of other factors. Even if their blood pressure, blood sugar and cholesterol appear within the normal range, excess weight is still a risk factor,” said lead author Dr Camille Lassale, from Imperial’s School of Public Health and now based at University College London.

Obesity is more dangerous than a lack of fitness

This study backs up another one from 2015, which 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.

What's the takeaway?

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 these studies drew their measurements.

It should be noted that the 2015 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, these studies are eye-openers and could rewrite the book of how we think about health and fitness on the whole. They further emphasize just how dangerous being overweight can be.

Editor's note: This article has been updated since it was originally published in December 2015.