People who are overweight but physically healthy have the same heart disease and cancer risk as normal weight people, according to US research.
Provided people exercise and are "metabolically fit" with a healthy blood pressure, cholesterol and blood sugar –– they are at no greater risk of serious illness.
Researchers from the University of South Carolina studied 43,000 people. A third of those were obese and of those, 46 percent were found to be metabolically healthy after a physical and lab test.
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This subset of healthy obese people generally exercised more than the unhealthy obese people and did not have high cholesterol, high blood pressure or obesity. Their risk of dying from cancer or heart disease was the same as people with a healthy weight –– and up to half that of the unfit obese 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," said study author Dr Francisco Ortega in a media 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."
Dr Ortega said the study highlights the importance of regular exercise.
"We believe that getting more exercise broadly and positively influences major body systems and organs and consequently contributes to make someone metabolically healthier, including obese people," he said.
Professor Helen Truby from the Monash University Faculty of Medicine, Nursing and Health Sciences, told ninemsn that people's risk of cardiovascular disease from obesity is a bit of a genetic lottery.
"There are a group of people who, if they undertake quite a lot of daily physical activity, are protected against having some of those higher cardiovascular risk types," she said.
"It's probably the fact their genes help them avoid some of those classic heart disease risks that we know obesity brings, such as type 2 diabetes, high blood levels of cholesterol, high triglycerides."
But Professor Truby said the message to take from this study is that everyone can benefit from regular exercise.
"It doesn't necessarily mean that even though you're undertaking a reasonable amount of activity that you are not going to get heart disease if you are genetically programmed to. It does mean that having some exercise every day is important," she said.
The best way to tell if you're at risk is by measuring your waist circumference.
"That gives you an element of measurement of the amount of fat stored around your trunk," she said.
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"If you have quite a lot of tummy fat, you are more likely to have more metabolic problems associated with your obesity than you are with someone who has fat around their hips."