Tissue components of weight loss in cancer patients. A new method of study and preliminary observations

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Abstract
A new approach using anthropometric, radiographic, biochemical, and ultrasonic methods allowed partition of body weight into fat, fat-free mass, skeletal muscle, and volume of heart, liver, kidneys, spleen, and tumor. These methods were used to evaluate body composition longitudinally in a pilot group of nine cancer patients, seven of whom lost weight (greater than 2.5 kg) during the study period. Two control groups also underwent the protocol: (1) healthy subjects (+/- 10% IBW) of similar age, sex, and height; and (2) patients with weight loss due to anorexia nervosa. Weight loss in both the cancer and anorexia nervosa groups could be accounted for primarily by loss in fat and skeletal muscle; although the relative magnitude of these tissue losses were approximately the same in both groups, cancer patients lost relatively less body weight. This was because (1) overt or occult ascites (detected radiographically) was present in cancer patients (3 of 9); (2) tumor bulk increased fat-free mass by up to 1 to 2 kg; and (3) the proportional loss in visceral organ volume was less in cancer patients than in anorexia nervosa patients. In the latter group, heart, liver, kidneys, and spleen were reduced in proportion to body weight, whereas in the cancer group as a whole, these organs (when uninvolved with tumor) lost little (heart and kidneys) or no volume (liver and spleen). This initial study suggests that the principal endogenous energy and nitrogen sources during evolution of weight loss in cancer are primarily adipose tissue triglycerides and skeletal muscle proteins. In some cancer patients, fluid accumulation, a large tumor burden, and the slow rate of visceral organ atrophy make body weight an unreliable index of available energy-nitrogen reserves.