MONDAY, May 2 (HealthDay News) -- Even normal-weight people with belly fat and heart disease have an increased risk of death compared to folks whose fat is concentrated elsewhere, a large, new study reports.

A "beer belly" or "muffin top" is as significant a risk factor as smoking a pack of cigarettes a day or having very high blood cholesterol, the study said. And the risk is greater for men.

That spare tire is even more significant than your overall body mass index (BMI, a ratio of weight to height) in predicting risk of death, the researchers said, noting their findings discount a puzzling theory known as the "obesity paradox." That surprising finding from earlier studies linked a higher BMI and coronary artery disease with better survival chances than normal-weight people.

"We suspected that the obesity paradox was happening because BMI is not a good measure of body fatness and gives no insight into the distribution of fat," said study lead author Dr. Thais Coutinho, a cardiology fellow at the Mayo Clinic in Rochester, Minn.

"BMI is just a measure of weight in proportion to height. What seems to be more important is how the fat is distributed on the body," she said in a clinic news release.

The study is published in the May 10 issue of the Journal of the American College of Cardiology.

The researchers looked at data from five studies conducted around the world, involving almost 16,000 people with coronary artery disease. The risk of death was nearly doubled for people with coronary artery disease and central obesity, which was determined by waist circumference and waist-to-hip ratio, the study found.

What exactly is the difference between belly fat and thigh fat, for instance?

"Visceral [belly] fat has been found to be more metabolically active," Dr. Francisco Lopez-Jimenez, the study's lead investigator and director of Mayo's Cardiometabolic Program, explained in the news release. "It produces more changes in cholesterol, blood pressure and blood sugar. However, people who have fat mostly in other locations in the body, specifically the legs and buttocks, don't show this increased risk."

Doctors should look beyond BMI in assessing patients' health risks and advise those with a large waist or a high waist-to-hip ratio to lose weight, even if they have normal BMIs, the study authors said. A BMI of between 18.5 and 25 is considered normal; between 25 and 29.9 is overweight; and a BMI of 30 or more is obese.

"All it takes is a tape measure and one minute of a physician's time to measure the perimeter of a patient's waist and hip," Coutinho said.

The study participants came from the United States, Denmark, France and Korea, and that diversity gives real-world applicability to the findings, Coutinho said.

More information

For tips on weight loss, visit the U.S. National Library of Medicine.