People with coronary artery disease are at greater risk of dying if they have fat around the waist, a study has found.
Researchers said sufferers with even a "modest" beer belly or muffin top have up to twice the risk of dying compared with those whose fat collects elsewhere.
The effect was even observed in patients with a normal Body Mass Index (BMI) who had just a thin layer of flab around their midriff.
The waist circumference and waist-to-hip ratio of nearly 16,000 people were analysed by researchers from the Mayo Clinic in the US as part of the study.
They found that carrying fat around the belly was potentially as dangerous as smoking a pack of cigarettes per day or having very high cholesterol.
Previous studies have shown that patients with a higher BMI and chronic diseases such as coronary artery disease have better survival odds than normal-weight individuals. However, the latest findings go against this "obesity paradox", researchers said.
"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 Thais Coutinho, the study's lead author. "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."
Francisco Lopez-Jimenez, from the Mayo Clinic, said stomach fat may be more harmful because it is more metabolically active.
"Visceral fat has been found to be more metabolically active. 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."
Coronary artery disease patients who have normal BMIs should be urged to lose weight by their doctors if they have a large waist circumference or a high waist-to-hip ratio, the authors claimed.