New research suggests people who have a "spare tyre" around their waist are three times more likely to die of a heart attack or stroke, even if the rest of their body is slim.
And it seems men and women who carry fat around their waist are at greater risk even than people who are clinically obese.
US doctors believe it could be because overweight and obese people store more weight on their thighs and hips, which is a different type of fat that can be protective.
The researchers studied the body mass index (BMI) and waist-to-hip ratio of 12,785 people with an average age of 44 over a period of 14 years.
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The waist-to-hip ratio illustrates how much fat they store around their middle, while the BMI is an estimated measurement of their overall body fat.
By the end of the study, 2562 people had died. Of those, 1138 died from a cardiovascular issue, such as heart disease or stroke.
The researchers found that people with a healthy BMI but high waist-to-hip ratio were 2.75 times more likely to die from a heart attack or stroke than people who had a normal waist-to-hip ratio.
Obese people were 2.34 times more likely to die from a cardiovascular condition than the healthy participants — 0.41 percent less of a risk than those with a large girth.
"We knew from previous research that central obesity is bad, but what is new in this research is that the distribution of the fat is very important even in people with a normal weight," senior author Dr Francisco Lopez-Jimenez from the Mayo Clinic in Rochester, Minnesota, said in a media release.
"This group has the highest death rate, even higher than those who are considered obese based on BMI. From a public health perspective, this is a significant finding."
The authors presented their findings at the European Society of Cardiology’s annual congress in Munich.
"Many people today know their BMI –– our research shows that if a person has a normal BMI, this by itself should not reassure them that their risk for heart disease is low," Dr Lopez-Jimenez said.
"Where their fat is distributed on their body can mean a lot, and that can be determined easily by getting a waist-to-hip measurement, even if their body weight is within normal limits."
Dr Robert Grenfell, clinical issues director at the Heart Foundation, told ninemsn that this research doesn't mean you're not at risk if you're overweight.
"Being generally overweight is a risk factor for heart disease, but carrying weight around the middle is particularly dangerous," he said.
"Fat around your abdomen is fat around your vital organs –– your heart, kidneys, liver and pancreas. Having extra fat here stops the organs from doing their job properly."
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Belly fat causes the body to release chemicals that increase insulin resistance, which could lead to cardiovascular conditions.
"Even if your BMI is normal, a waistline of greater than 94cm for most men and 80cm for most women puts you at increased risk of developing chronic diseases like heart disease, type 2 diabetes and some cancers," Dr Grenfell said.