You can be fat AND fit, researchers say

(CNN) - "I'm in shape," you've probably heard people quip. "Round is a shape."

It's an old joke, but there may be some truth to it. A new study published this week in the European Heart Journal shows it is possible to be both obese and healthy.

"It is well known that obesity is linked to a large number of chronic diseases such as cardiovascular problems and cancer," lead study author Dr. Francisco Ortega said in a statement. "However, there appears to be a sub-set of obese people who seem to be protected from obesity-related metabolic complications."

The study

Researchers analyzed data from 43,265 participants in the Aerobics Center Longitudinal Study, which was done between 1979 and 2003.

The participants' body fat percentages were determined using hydrostatic weighing (submersion in water) or skinfold measures, and their fitness levels were tested on a treadmill. Using these criteria, 29.7% of the study participants were labeled obese. Of the obese, nearly half were considered "metabolically healthy."

All of the participants were followed until 2003; 1,779 died during that time period.

What's metabolically healthy mean?

Your metabolic health is determined by several factors: High blood pressure, high triglycerides, low HDL - or good - cholesterol and high fasting glucose levels. For this study, a participant was considered metabolically healthy if they displayed zero or only one of the above symptoms.

Ortega and his colleagues use several terms to describe the study participants who were obese but metabolically healthy. They call it "uncomplicated obesity" or "metabolically benign obesity." Basically that means the obese individuals saw few negative health effects of their extra weight.

The results

The researchers found that the metabolically healthy but obese participants had a 38% lower risk of dying than their metabolically unhealthy peers. There was also no risk difference between the metabolically healthy obese and the metabolically healthy normal weight participants.

"Our study, together with previous literature, strongly suggest that a better cardiorespiratory fitness will make you healthier regardless of your weight status," Ortega told CNN. "These findings clearly support the notion that doing exercise and improving fitness might be an effective public health tool for fighting against obesity."

Caveats

As in any research, there are limitations to the conclusions drawn from the results. Insulin resistance - a precursor of diabetes - was not measured in the study participants. The data also did not show how long the participants were obese, which can be an important predictor of metabolic risk, according to the study authors.

Still, one thing is clear to Ortega: "Exercise benefits everyone, regardless of fitness and fatness level. So exercise should be encouraged by doctors to all the patients."