NEW YORK (Reuters Health) – People with body mass indexes (BMI) that fall into the normal range may still have to be concerned about obesity, a cardiologist from the Mayo Clinic warns.

Dr. Francisco Lopez-Jimenez and his colleagues recently reported that people with normal BMIs but excess body fat were more likely to have high cholesterol, excess belly fat and other characteristics of the metabolic syndrome, a set of symptoms that puts people at greater risk of heart disease and diabetes. BMI is the ratio of height to weight that is frequently used to determine if an individual is over-weight or under-weight.

This condition, which Lopez-Jimenez and his team have termed “normal-weight obesity,” was extremely common; they found it in 61 percent of a sample of 2,127 men and women with normal BMIs.

“It seems like it affects adults of all ages, men and women, and pretty much all races, according to our subgroup analysis,” the researcher told Reuters Health. “The problem affects pretty much everybody.”

Sedentary living is usually the factor responsible for causing muscle mass to dwindle as fat accumulates, he added. “It usually comes down to exercise.”

High body fat is defined as above 20 percent for men and above 30 percent in women. The best way to find out one’s own body fat percentage, Lopez-Jimenez told Reuters Health, is to use a reliable bioelectrical impedance machine. These machines can now be found at many doctors’ offices and spas, he said, and can evaluate body fat percentage in less than a minute.

An older method for gauging body fat, in which calipers are used to measure skin fold thickness, is more time consuming and less reliable, according to Lopez-Jimenez. And while many people with normal weight obesity have high waist circumferences based on current guidelines (over 102 centimeters for men, over 88 cm for women), some don’t, he said, so waist size isn’t a reliable indicator.

He and his colleagues are now investigating what people with normal-weight obesity can do to replace their excess body fat with lean mass. “Whatever means a person has to increase their muscle mass and burn calories, that will be very likely the best way to deal with it,” Lopez-Jimenez said.

Exercise will certainly be important, he added, and it’s likely that people should incorporate both strength training and aerobic workouts into their regimen of physical activity.

SOURCE: Mayo Clinic Women’s HealthSource, September 2008.