A theoretical analysis using ratios of the major elements measured by neutron activation analysis to derive total body water, protein, and fat.

A theoretical analysis based upon Reference Man is used to derive the water, protein, and fat components of soft tissue using the ratios of carbon/oxygen and nitrogen/hydrogen determined by in vivo neutron activation analysis and measurement of body mineral content by dual energy x-ray absorptiometry. The standard deviations in the estimates of water, protein, and fat are 0.58, 0.59, and 0.53 kg, respectively, if the reproducibility measurement of the carbon/oxygen ratio is 2.5% and of the nitrogen/hydrogen ratio is 5%, the accuracy of measurement of bone mineral is 4%, and estimate of glycogen is 0.5 kg. New neutron activation technology may permit sufficiently precise measurements.