Experience in the use of body composition studies in gastroenterology

The measurement of total body nitrogen (TBN) as an index of total protein in the body has been performed in a number of different studies. The in vivo technique is based on the detection and counting of the characteristic nitrogen gamma rays emitted after neutron capture. The accuracy of the method was estimated as better than 10%, reproducibility was 5.5%. The effective dose equivalent for nitrogen measurement is 50 mrem. TBN was initially measured in 121 volunteers and found to correlate best with the mean of height and arm span (HAS), a better estimate of skeletal size than height alone. This was then used to normalize TBN for body size with the derivation of a Nitrogen Index (NI), with a normal range of 0.8 - 1.2. A select group of 38 malnourished patients were treated with total parenteral nutrition for periods of 3 to 33 months. This resulted in a weight gain of 10% and a significant increase of 32% in TBN. In contrast, increases in lean body mass, measured anthropometrically and total body potassium (TBK) were only increased 9%, the later two reflecting total and intracellular water respectively, but not protein content