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Some fit obese individuals have no greater risk for chronic disease than normal weight people

Think food is a well-deserved reward for putting in time at the gym? Fat chance. It's true that vigorous exercise burns calories, but studies show that people overestimate just how many. Studies show that running a mile, for example, is believed to burn about 450 calories, whereas in reality it burns only 110 or so calories - about one-quarter worth of a bran muffin. istockphoto

(CBS News) Usually being obese means a higher chance of developing health problems. But, a new study shows that it is possible to be fat and fit - and also to be at no greater risk for some chronic diseases.

People who were deemed "metabolically healthy" obese individuals - meaning they had no insulin resistance, diabetes, high cholesterol or blood pressure issues - had a lower risk of death than unfit obese individuals. They had no greater risk of death than normal weight fit people.

"It is well known that obesity is linked to a large number of chronic disease such as cardiovascular problems and cancer. However, there appears to be a sub-set of obese people who seem to be protected from obesity-related metabolic complications," first author Dr. Francisco Ortega said in a press release. "They may have greater cardio-respiratory fitness than other obese individuals, but, until now, it was not known the extent to which these metabolically healthy but obese people are at lower risk of diseases or premature death."

The study was published in the European Heart Journal on Sept. 4.

The 43,265 participants in the study were all part of the "Aerobics Center Longitudinal Study" (ACLS) between 1979 and 2003. The study participants were 98 percent white and mostly worked in executive or professional positions. About one fourth of the subjects were women.

Each subject completed a detailed questionnaire on their medical and lifestyle history, had a physical examination that included a test on their cardio-respiratory fitness and had measurements of height, weight, waist circumference and body fat percentage taken. Blood pressure, cholesterol and fasting glucose levels were also recorded. The researchers followed the subjects from when they entered the study until they died or until 2003.

Out of all the obese subjects, 46 percent were deemed "metabolically healthy." When all factors were accounted for, 38 percent of metabolically healthy yet obese people had a lower risk of death than their metabolically unfit obese peers. They also had no significant increased death risk compared to metabolically fit, normal weight participants.

It's important to note that these "metabolically fit" obese individuals regularly exercised and had a higher level of fitness than most obese people.

""There are two major findings derived from our study," Ortega said. "Firstly, a better cardio-respiratory fitness level should be considered from now on as a characteristic of this subset of metabolically healthy obese people. Secondly, once fitness is accounted for, our study shows for the first time that metabolically healthy but obese individuals have similar prognosis as metabolically healthy normal-weight individuals, and a better prognosis than their obese peers with an abnormal metabolic profile."

The researchers suggested that physicians should pay closer attention to body fat percentage and fitness levels when assessing a patients risk for cardiovascular disease and cancer.

"It is possible to be fat and fit -- but relatively few people are," Dr. David Katz, director of the Prevention Research Center at Yale University School of Medicine, told HealthDay. He was not part of the study.

"It is certainly possible to be thin and unhealthy, which is why health, not a particular weight, is what we should be aiming for as both individuals and a society," he said.

Amy Thompson, a senior cardiac nurse with the British Heart Foundation, added to the BBC that it's important to remember that for the majority of people obesity is an "undeniable risk factor" for coronary heart disease. Keeping tabs on your body mass index and measuring your waist while maintaining a healthy diet and fitness regiment are some ways to help keep your risk lower.

"It is particularly important to be aware of your weight if you are carrying excess fat around your middle," she said. "The fat cells here are really active, producing toxic substances that cause damage which can lead to heart disease."