Measurement of body composition of live rats by electromagnetic conductance

Measurement of body composition in vivo is important in many nutritional studies. One method for estimating body composition is total body electrical conductance (TOBEC). The TOBEC methodology is based on measuring changes of an electromagnetic field that are proportional to lean body mass (LBM). Sprague-Dawley rats (n = 117) ranging in age from 49 to 105 days were measured by TOBEC, and the TOBEC results were compared with direct carcass chemical analyses. The rats ranged in weight from 155 to 500 g. Mean LBM was 92.4% of total body weight (b.wt.), and mean body fat was 7.4% of total b.wt. Mean hydration of LBM was 71.7% and decreased (r = -0.59, p < 0.0001) with age. Using the manufacturer's supplied equation, TOBEC measurement underestimated actual LBM by 12% (p < 0.0001). As a consequence of this error, a new prediction equation was generated using half of the data set, and this equation was cross-validated with the other half of the data set. The mean LBM calculated from the new prediction equation was not different from chemically determined LBM, but the estimated percent body fat of some rats was negative. Thus, TOBEC may be useful in predicting mean LBM of a population, but this indirect method may lack the sensitivity to provide accurate estimates of body composition of an individual.