An improved calibration for the in vivo determination of body nitrogen, hydrogen, and fat

Abstract

Additional investigation of an original technique for measuring total body N by prompt .gamma. neutron activation demonstrated the need for certain changes in the calibration procedures to apply the method to studies of patients with abnormal metabolism. Total body N, hydrogen and fat were derived, simultaneously, from data obtained by neutron capture .gamma.-ray analysis combined with the measurements of body weight, total body weight and total body Ca. In this improved calibration technique, total body N is more accurately measured, not only in normal subjects, but also in obese subjects and in patients with marked changes in hydration, such as cancer patients. The fat values calculated do not rely on a fixed relationship of total body water or total body K when lean body mass as in the previous studies, but are calculated as the difference between body weight and the sum of body water, protein and bone mineral ash. This improved technique was applied to the study of 3 groups of subjects: the general population with a normal weight distribution, and 2 extremes represented by obese and cancer patients.