Normal weight obesity isn't an oxymoron.

"The definition of obesity is having excess fat, not excess weight," says Francisco Lopez-Jimenez, M.D., Mayo Clinic cardiologist, in the September issue of Mayo Clinic Women's HealthSource.

Dr. Lopez-Jimenez was the lead researcher in a Mayo Clinic study that found more than half of Americans who are considered normal weight have high levels of body fat. Women with more than 30 percent body fat and men with more than 20 percent are considered obese, even if they have a normal body mass index.

Typically, obesity is determined by calculating body mass index (BMI) using height and weight. "This makes a lot of sense on the surface because people with excess weight for their height often are at high risk of health problems, but it doesn't tell the whole story," says Dr. Lopez-Jimenez.

The calculation of body fat determines how many pounds of body weight correspond to fat. The most common technique to measure body fat is bioimpedance, a method that uses an electrical current to look at body composition. These measurement devices are available at many fitness centers and some clinics.

The Mayo Clinic study, which looked at 2,127 people with normal BMI levels, found that those who had the highest body fat were at increased risk of high blood pressure, high levels of triglycerides (a type of blood fat) and abnormal cholesterol levels and insulin resistance. These metabolic abnormalities significantly increase the risk of type 2 diabetes and cardiovascular disease.

Another way to determine an unhealthy level of body fat is by measuring your waist. In women, a waist measurement of 35 inches or more indicates an increased risk of developing obesity-related health problems.

The solution to excess body fat, even for those of normal weight, is to exercise more and eat a healthier diet.

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