Body composition: An update on older and current technology

The laboratory techniques for the measurement of body composition have been available for more than 50 years. However, the desire to obtain body composition information for the lay public has only recently become popular. This is especially prevalent with the advent of low cost body composition analyzers from Tanita and Omron. The standard procedure to determine if a person is obese is to determine their Body Mass Index (BMI). Values above 25 (kg/m2) are considered above normal. However, the efficacy of BMI as a means of evaluating relative fatness in a total population is questionable. Data from our laboratory at USC indicate approximately 10-15% of a college-age population are miss-diagnosed by BMI, when compared to body composition measured by hydrostatic weighing. Bio-impedance (the prediction of fat from electrical resistance) was shown to be a more viable alternative to BMI in our research, as well as others. The classical laboratory method of measuring body composition is densitometry (hydrostatic weighing). However, this technique requires intense subject involvement (water immersion) and requires the additional measure of residual lung volume. In addition, this technique is not considered accurate for children under 15 years of age. An alternative method to measure body density by air displacement has been available (Body Box or BOD POD). Howver, the cost of this device is approximately $75,000 US and thus may be inappropriate for many laboratory technique. This method employs the use of X-Rays to measure tissue density. The method appears to have promise, but again, the cost of the device is well in excess of $120,000 US. Bio-impedance devices have the benefit of being both inexpensive and portable - useable in the field as well as the laboratory. The classical method of measuring body composition by this technique is to measure electrical resistance of the body from hand to foot (total body). This method has been shown to have SEE of approximately 3-4% body fat, when compared to hydrostatic weighing. Two new impedance analyzers, the Tanita and Omron, measure electrical resistance regionally, across the legs (Tanita) and arms (Omron). These analyzers are inexpensive ($100-200 US) and easy to use, making them ideal for the general public. Our research has shown these analyzers to have substantial variability. Of a college-age population of 200 students, almost 40% of these subjects had predictive errors (compared to hydrostatic weighing of 5% body fat. Anthropometry such as skinfolds is another viable technique and is perhaps the most popular choice for health clubs and fitness trainers. Skinfolds may also be the most accurate estimate of body composition for young children. Copyright © 2001 The Hong Kong Institute of Education.