1. Two groups of adult men were studied in Bangalore, India, under identical conditions: the ‘normal weight’ subjects (mean body mass index 20.8 kg/m2) were medical students of the institute with access to habitual energy and protein intakes ad libitum. The other group, designated ‘undernourished’, were labourers on daily wages (mean body mass index 16.7 kg/m2).
2. In an earlier study we obtained lower absolute values for both basal metabolic rate and protein synthesis in the undernourished subjects; however, when the data were expressed on a body weight or fat-free mass basis, a trend towards higher rates of protein synthesis, as well as higher basal metabolic rate, was evident. The suggestion was made that such results reflected the relatively higher energy intakes per kg body weight of the undernourished subjects on the day of study. The objective of the present study was therefore to control for the dietary intake during the measurement of whole body protein turnover.
3. In the present study dietary intakes were equated on a body weight basis; however, expressed per kg fat-free mass, the normal weight subjects had received marginally higher intakes of energy and protein. The results, however, were similar to those of the previous study. In absolute terms, basal metabolic rate, protein synthesis and breakdown were lower in the undernourished subjects. When expressed per kg body weight or per kg fat-free mass, the undernourished subjects had higher basal metabolic rates than the well-nourished subjects, whereas no differences were seen in the rate of protein synthesis or breakdown.
4. Estimates of muscle mass, based on creatinine excretion, indicated that the undernourished subjects had a higher proportion of non-muscle to muscle mass. Nitrogen flux (Q) was determined from 15N abundance in two end products, urea (Qu) and ammonia (Qa). The ratio Qu/Qa was increased in the undernourished subjects and was significantly correlated with the ratio of non-muscle to muscle mass (r = 0.81; P < 0.005). These results fit in with our earlier suggestion of a greater proportion of non-muscle (visceral) mass in undernourished subjects.
5. The present data suggest that there are no changes in the rate of protein synthesis or breakdown in chronic undernutrition when results are expressed, conventionally, per kg fat-free mass. It can be theoretically shown, however, that there could be a 15% reduction in the rate of turnover of the visceral tissues in chronic undernutrition. This, together with the reduced urinary nitrogen excretion, would contribute to nitrogen economy in these individuals.