People who are normal-weight but carry a good deal of body fat may be at increased risk of heart disease and stroke, a small study suggests.

Most people have by now heard of body mass index (BMI), a measure used to classify people as normal-weight, overweight or obese based on their weight and height.

However, there are people who are technically normal-weight based on their BMI yet have a substantial amount of excess fat, and some researchers say this is its own type of "syndrome."

In research published last year, a group of Italian researchers described what they call "normal-weight obese" or NWO syndrome -- where BMI is normal but body fat makes up more than 30 percent of weight.

The good news for these individuals is that they don't have the metabolic conditions that often mark obesity -- such as high blood pressure, unhealthy cholesterol levels and high blood sugar.

On the other hand, the bad news, according to this latest study, is that people with NWO syndrome may be prone to high blood levels of certain inflammation-related proteins. That suggests they are at risk of becoming obese or developing cardiovascular disease in the future, the study authors report in the American Journal of Clinical Nutrition.

Dr. Antonino De Lorenzo of the University of Tor Vergata in Rome led the research team, the same one that first described NWO syndrome.

The study included 20 young women who met the definition of NWO syndrome, along with 20 normal-weight women and 20 who were overweight based on their BMI and had a body fat percentage greater than 30 percent.

Overall, the researchers found, the NWO group had higher levels of several inflammatory proteins than normal-weight women did. The excess body fat in the former group may explain the difference, as research suggests that fat tissue secretes inflammatory substances, De Lorenzo and his colleagues note.

Because inflammation has been implicated in the buildup of artery-clogging plaques, women who have a normal weight but high fat mass may be at increased risk of heart disease and stroke down the road, according to the researchers.

What's more, they point out, these women are likely to have a false sense of security about their heart health because their BMI is normal.]

This means that measuring body fat percentage, and not just BMI, could be an important part of preventing obesity-related ills, the researchers conclude.

SOURCE: American Journal of Clinical Nutrition, January 2007.