Bioelectrical Impedance Analysis Conference Proceedings Published

Proceedings from the National Institutes of Health Consensus Development Conference on Bioelectrical Impedance Analysis (BIA) were published in the September 1996 supplement issue of the American Journal of Clinical Nutrition. The conference, held on December 12-14, 1994, brought together a panel of scientific experts to assess the use of BIA for body composition measurement. The panel examined the accuracy and validity, safety, technique and standardization, clinical applications, and future directions for this technology. A conference statement provides an overview of the objectives and conclusions of the meeting, and the conference proceedings provide practitioners with a comprehensive source document on the subject of BIA.

BIA is a relatively simple, quick, and noninvasive method for estimating body composition. The technology is currently used in diverse settings, including private clinicians' offices, health clubs, and hospitals, and across a spectrum of ages, body weights, and disease states. Despite a general public perception that BIA measures "body fat," the technology actually determines the electrical impedance of body tissues, which provides an estimate of total body water (TBW). Using TBW values derived from BIA, one can estimate fat-free mass (FFM) and body fat (adiposity). Because different methodologies and machines are used to measure BIA, calculations of an individual's body fat may vary by as much as 10 percent of body weight.

The panel concluded that BIA provides a reliable estimate of TBW under most conditions. It can be a useful technique for body composition analysis of healthy individuals and of persons with chronic conditions such as mild-to-moderate obesity, diabetes mellitus, and other medical conditions in which major disturbance of water distribution are not present. However, its accuracy is limited when estimating body fat in the severely obese. In addition, BIA is not useful in measuring short-term change in an individual's body composition, such as in response to diet or exercise.

The panel recommended that the variables affecting BIA measurements be standardized and controlled for more reliable BIA readings. Specific areas for standardization examined by the panel include body position, hydration status, consumption of food and beverages, skin and room temperature, and recent physical activity. In addition, because a specific, well-defined procedure for performing routine BIA measurements is not practiced, the panel recommended that a committee of appropriate scientific experts and instrument manufacturers be formed to set instrument standards and procedure methods. To obtain a copy of the supplement issue on BIA, contact the American Journal of Clinical Nutrition, 9650 Rockville Pike, Bethesda, MD 20814-3988; phone (301) 530-7038, fax (301) 571-8303, or e-mail journal@ascn.faseb.org. The NIH BIA in Body Composition Measurement Technology Assessment Conference Statement is available on the Internet at http://consensus.nih.gov. Copies of the statement are also available through WIN.