We agree with Dr. Frühbeck that in this era of epidemic obesity trends, studies citing a lack of weight assessment in the clinical setting are concerning. The current medical literature suggests that timely diagnosis and treatment of obesity may prevent considerable morbidity among U.S. adults. Our goal in addressing obesity measures, therefore, was to identify a screening tool that can be widely applied in clinical practice.

Although BMI has limitations, currently it is the most appropriate initial screening instrument. Other measures may more accurately estimate body fat but are expensive and time-consuming. In clinical practice, BMI is easily calculated on the basis of standard measures that generally show little interobserver variation. Evaluation of BMI is inexpensive and requires minimal training, and results are immediately available. As a measure of obesity, BMI is very frequently used in the mass media and is thus familiar to many patients.

We recognize that BMI has disadvantages as a measure of health risk. Although generally correlated closely with body fat, it does not measure fat itself. The degree of error may vary with sex, ethnicity, and fat-free mass. However, the cutoff of at least 30 kg/m² is a risk-based criterion, linked with an approximately 2-fold mortality risk. Similarly, BMI has been linked with a wide range of adverse health consequences (more so than other anthropometric measures). Thus, BMI has clear clinical utility. Although BMI does not provide information about fat distribution, it may be augmented by waist circumference (which identifies central weight accumulation) among persons with nonobese BMIs whose cardiovascular risk is uncertain.

Dr. Frühbeck also raises a concern that BMI may not be the appropriate measure to track after obesity intervention. Because the U.S. Preventive Services Task Force is charged with addressing screening, not treatment, such a consideration is beyond the scope of its review and recommendations. We do note that most of the intervention trials we reviewed used weight as the primary outcome and identified a degree of loss necessary for improved clinical end points. Since interventions typically included exercise, this outcome reflects both the effect of fat loss and muscle gain.

No screening test for excess body weight is ideal, but recent data suggest that all too often no test is applied. The ease, rapidity, and low cost of routine BMI calculation may facilitate the transition of obesity onto the already-busy docket of a practicing clinician.