Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 9/30/1997
Publication Date: N/A
Interpretive Summary: The bioelectrical impedance or bioimpedance method is gaining increased acceptance in routine nutritional assessment of healthy individuals and in clinical practice. This method is attractive because it is practical, portable, and cost-effective. The bioimpedance method has been effectively used to determine body fluid volumes and body composition. Recent evidence indicates that the bioimpedance method is an accurate and sensitive method for measuring change in body composition in patients who are losing body weight and muscle mass because of infectious disease. Also, it a valid method for assessment of body composition during weight loss. Although a variety of mathematical models are used to translate bioimpedance data into body composition variables, recent studies show that all models yield similar body composition values. One limitation of the bioimpedance method is the inability to accurately determine regional body fluid accumulation with the current electrode placements on the hand and feet. Studies in which electrodes are relocated to the site of the fluid accumulation indicate the validity and accuracy of the technique. Another potential drawback also relates to body geometry. It is suggested that the bioimpedance method may be prone to errors in individuals with excessively long limbs (arms and legs) relative to the torso length. Overall, the use of the bioimpedance method is increasing, particularly among clinicians who seek to monitor body composition in patients with altered fluid status and weight loss. This information will be useful to nutrition researchers and medical practitioners who want to monitor nutritional status and body composition of individuals who are changing body weight.
Technical Abstract: Although there is a long history of the use of electricity in medicine, only recently have the bioelectrical responses to administered alternating current been used to assess health and nutritional status by monitoring fluid volumes and body composition of humans. The bioimpedance method, which relies on the measurement of various impedance parameters in response to a single of multiple frequency alternating current, has been used in clinical nutrition assessment. This review presents the relations between impedance variables and biological measures of body composition, describes biophysical models for translation of bioimpedance variables into body compositional parameters, and compares the biophysical models for estimating body composition in patients with altered body composition. Overall, the bioimpedance method yields acceptable estimates of body composition in healthy individuals and patients with altered body composition. Two concerns that requires additional study include the effects of body geometry (i.e., limb lengths) and the effects of regional fluid accumulation on validity of the impedance method. Resolution to these problems may be found in the use of different electrode placements than are presently used. The increased use of the bioimpedance method in clinical nutrition research reflects the need of the medical community to assess human body composition during acute illness and catabolic disease. Evidence from clinical trials supports the validity and accuracy of the bioimpedance method.