Metabolic Syndrome: Not Just for the Obese

St-Onge M-P, Janssen I, Heymsfield SB. Metabolic syndrome in normal-weight Americans: new definition of the metabolically obese, normal-weight individual. Diabetes Care. 2004;27:2222-2228.

Even a slightly elevated body mass index (BMI) may render a normal-weight individual metabolically obese--that is, at risk for the metabolic syndrome, propose St-Onge and colleagues. Clinicians should screen persons in the "normal to slightly elevated range" of BMI for metabolic abnormalities, as research indicates that increases in BMI correlate with rising prevalence of the metabolic syndrome.

Study subjects were drawn from the sample used in the Third National Health and Nutrition Examination Survey between 1988 and 1994. A total of 7,602 participants--who were at least 20, were not pregnant, and had a BMI within the targeted range of 18.5 to 26.9 kg/m ²--were used in the analysis.

The prevalence of the metabolic syndrome rose with each incremental increase in BMI--independent of sex and after controlling for factors such as age, ethnicity, physical activity, smoking, and intake of alcohol, fat, and carbohydrates. Compared with men who had a BMI of 18.5 to 20.9 kg/m², those with a BMI of 21.0 to 22.9 kg/m², 23.0 to 24.9 kg/m², and 25.0 to 26.9 kg/m² had odds ratios (ORs) for the metabolic syndrome of 2.97, 4.95, and 9.88, respectively. In the corresponding BMI categories among women, respective ORs were 3.68, 7.51, and 18.58.

When the individual components of the metabolic syndrome were considered, persons with a higher BMI had a greater risk of both high triglyceride levels and low HDL cholesterol levels. Prevalence of high blood pressure (ranging from 6.6% to 41.5%) varied according to BMI, ethnicity, and sex. An elevated plasma glucose concentration was the least prevalent component throughout the study population; rates were less than 12% in all sex and ethnic categories.

The authors attribute the increased risk of the metabolic syndrome in normal-weight persons to genetics or body composition abnormalities. Regardless of the etiology, they conclude that "current recommendations for weight loss may need to be modified and that weight loss in individuals with BMI < 25.0 kg/m² should be considered if they also have the metabolic syndrome."