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People with a normal weight but extra pounds around the middle may have lower long-term survival odds than individuals who are obese, a new study suggests.

A normal weight for an adult is often calculated using the body mass index (BMI), a measurement of weight relative to height. For the new study, researchers focused on people’s waist-to-hip ratio, which measures whether they’re storing excess fat around the middle.

They found that men with a normal BMI but central obesity, the clinical term for belly fat, had twice the mortality risk of men who were rated overweight or obese according to BMI standards. Normal-weight women with belly fat, meanwhile, had a 32 percent higher mortality risk than obese women without excess pounds around the middle.

“Waist size matters, particularly in people who are a normal weight,” said senior study author Francisco Lopez-Jimenez of the Mayo Clinic in Rochester, Minn.

“The lack of recognition of this leads people with abnormal distribution of fat to have a false sense of safety or reassurance that they don’t need to exercise or [that] they can eat whatever they want because they are ‘skinny,’ when in reality, if a person has a normal BMI and an abnormal waist size, the risk is worse than if they have a high BMI.”

To understand the connection between waist size and mortality, researchers analyzed data on more than 15,000 adults.

Based on BMI, about 40 percent of the people were of normal weight, while 35 percent were overweight and 25 percent were obese. Using World Health Organization criteria, about 70 percent were considered centrally obese.

Over an average of about 14 years, there were 3,222 deaths, including 1,404 due to cardiovascular disease. A man with normal-weight central obesity had a 78 percent higher risk of death from cardiovascular disease than a man with a similar BMI but no fat around the middle, the study found. For women, normal-weight central obesity more than doubled the risk of death from cardiovascular disease.

The findings, published in the Annals of Internal Medicine, provide ample evidence suggesting that doctors look beyond BMI to identify people who are at the greatest risk due to excess pounds, Paul Poirier of the Quebec Heart and Lung Institute noted in an editorial.

Measuring BMI is a good start for identifying patients at greater cardiovascular risk, but it is not sufficient to identify every person at risk, Poirier wrote. “We need to talk about waist loss and not weight loss,” he said by e-mail. “When you lose weight through exercise and proper nutrition, then the first fat to go is the fat at the waistline.”

Some preliminary research has pointed to the potential for diets low in carbohydrates to help eliminate waist fat, though more study on this is needed, Lopez-Jimenez noted.

— Reuters