Just because you're of normal weight, doesn't mean you don't have hidden fat around your belly that could increase your risk of death, a new study suggests.

Researchers from the Mayo Clinic found that people of normal weight with belly fat -- meaning a high waist-to-hip ratio -- actually have a higher risk of dying than people who are obese.

"The high risk of death may be related to a higher visceral fat accumulation in this group, which is associated with insulin resistance and other risk factors; the limited amount of fat located on the hips and legs, which is fat with presumed protective effects; and to the relatively limited amount of muscle mass," Dr. Karine Sahakyan, M.D., Ph.D., a cardiovascular research fellow at the Mayo Clinic, said in a statement.

Sahakyan and her colleague, Dr. Francisco Lopez-Jimenez, M.D., a cardiologist at the Mayo Clinic, analyzed the health statuses of 12,785 adults who participated in the Third National Health and Nutrition Examination Survey. The researchers separated everyone into three groups based on their body mass indexes -- normal weight, overweight and obese -- and then into two groups based on the ratio of their waists to their hips -- normal and high.

The researchers followed up 14.3 years later, and found that people who were of normal weight, but who had "central obesity" had a 2.75 times higher risk of dying from heart-related reasons, and a 2.08 times higher risk of just dying in general. This is compared with people who had a "normal" waist-to-hip ratio, and a normal BMI.

Meanwhile, people who were obese who had a "normal" waist-to-hip ratio had a 1.41 times increased risk of dying, and people who were obese who had a "high" waist-to-hip ratio had a 2.34 times increased risk of dying.

The study was presented at the European Society of Cardiology Congress; it has not yet been published in a peer-reviewed journal, which means the findings should be considered preliminary.

However, other published studies have shown a similar relationship. A 2008 study in the New England Journal of Medicine showed that people with the most belly fat had a doubled risk of early death compared with people with the least belly fat, WebMD reported.

"Our study shows that accumulating excess fat around your middle can put your health at risk even if your weight is normal," study researcher Dr. Tobias Pischon, M.D., M.P.H., told WebMD. "There aren't many simple individual characteristics that can increase a person's risk of premature death to this extent, independent of smoking and drinking."

So what's there to do if you want to blast that belly fat? USA Today reported on a Duke University study last year, which showed that aerobic exercise trumps resistance training to get rid of this particular kind of fat.