A new method for the rapid measurement of body composition in critically ill surgical patients

A rapid, non-invasive method for the measurement of absolute amounts of fat, protein, minerals and water in the body has been developed which is applicable to very ill patients. The patient is weighed and skinfold thickness is measured with calipers. The body contents of potassium, nitrogen, sodium, chlorine, calcium and phosphorus are measured in a whole-body radiation counter after irradiation with fast neutrons. From these values absolute amounts of body fat, protein, minerals and water are calculated. The procedure, which takes about 40 min, is carried out with the patient lying supine on a couch. The errors in the absolute measurement of the components expressed as percentages of body weight are: for fat, 4.5 per cent; for protein, 1.6 per cent; for minerals, 0.8 per cent; and for water, 4.9 per cent. The radiation dose is equivalent to that of a chest radiograph (50 mrem). We have used this technique (a) to determine the tissue composition of the weight lost in 16 patients after excision of the rectum; (b) to establish that the weight gained by 16 patients receiving intravenous nutrition was mainly water; and (c) to show that in 10 patients who received a simple solution of amino acids for 2 weeks after rectal excision body protein was preserved as efficiently as in 10 similar patients who received a full course of intravenous nutrition. This is the first time body weights of living persons have been broken down into terms of fat, protein, minerals and water, and the method should help to solve a number of metabolic and nutritional problems in clinical surgery.