Assessment and prevalence of obesity: application of new methods to a major problem.

Overweight and obesity are major health problems worldwide. A body mass index of > or =25 has been classified as overweight and of > or =30 as obesity. However, national and epidemiologic data on overweight and obesity are not based on actual measures of body fat because of the difficulty of collecting such data from large groups and especially from the obese. There are now numerous direct and indirect methods to assess body fat. Anthropometric techniques are the most common indirect methods used in epidemiologic and clinical assessments, but these are restricted in the obese to circumferences. The other methods of assessing body fat are bioelectrical impedance, body density, total body water, and dual X-ray absorptiometry, all of which have advantages and limitations when applied to the obese. All these methods make use of statistical models in calculating body composition. There are several sources of available reference data for anthropometric measures for the US population, but no direct measures of body fat are currently available. There is a clear need for the continued development and validation of new and existing techniques to determine levels of fat.