People who are average-size, but carry excess weight around their stomach, could be more at risk from health issues than those who are overweight, a new study suggests.
They found that men who carried a "spare tyre" were twice as likely to die than those defined as overweight or obese.
Meanwhile in women, the risk of death was increased by up to 40%.
The study showed that over a period of 14 years, normal-weight individuals with excess weight around their middles had a worse survival record than participants officially classified as overweight or obese.
The researchers, led by Dr Francisco Lopez-Jiminez from the Mayo Clinic, wrote in the journal Annals of Internal Medicine: "Our analyses .. show that normal-weight US adults with central obesity have the worst long-term survival compared with participants with normal fat distribution, regardless of BMI category, even after adjustment for potential mediators.
"Our findings suggest that persons with normal-weight central obesity may represent an important target population for lifestyle modification and other preventive strategies.
"Future studies should focus on identifying factors associated with the development of normal-weight central obesity and better understanding the effect of normal-weight central obesity on health outcomes."
The researchers pointed out that "spare tyre" obesity was associated with the accumulation of "visceral" fat around internal organs, which is known to be especially harmful to health.
Excess visceral fat was associated with insulin resistance - which can lead to diabetes - higher levels of cholesterol and blood fats, and inflammation.
Study participants, who had an average age of 45, were recruited for the Third National Health and Nutrition Examination Survey (NHANES III), an on-going investigation collecting health and lifestyle data in the US.
Christopher Allen, senior cardiac nurse at the British Heart Foundation, said: "We all know that watching our weight is important, but often it's forgotten that where you carry the weight makes a difference too. Having more fat around your middle can lead to Type 2 diabetes, which greatly increases your risk of having a heart attack or stroke, but there is lots you can do to get rid of this excess weight and lower your risk.
"Keeping physically active and eating a healthy, balanced diet will help control your weight and reduce your risk of diabetes and heart and circulatory diseases. If you're concerned about your weight or need further support, make an appointment to see your GP or practice nurse."
Of the 3,222 deaths recorded in the study, 1,404 were due to heart disease.