BASAL METABOLIC-RATE AND DIETARY SEASONALITY AMONG TIBETAN NOMADS

The results of 51 overnight measurements of basal metabolic rate (BMR) in a sample of pastoral nomads resident permanently in Phala, Tibet A utonomous Region, China, are reported. Past studies demonstrated a cul turally driven seasonality of diet, with very low summer and very high winter caloric intake. The study was designed to test the hypothesis that the ability of Phala nomads to subsist on low caloric intake for several summer months without signs of malnutrition is explained by lo wer summer BMR. However, BMR measurements of 40 nomads 13-69 years of age during the summer and remeasurement of 11 nomads during the winter of 1993 provide no evidence for low summer BMR to compensate for the low summer caloric intake. BMR in both seasons is within the normal ra nge predicted by international equations. The BMR of males does not di ffer from that of females, and the BMR of females averages 7% higher t han predicted. Anthropometric evidence reveals that the Phala nomads a ccumulate body fat during the winter. It is inferred that this may buf fer the summer period of low intake. The pattern of subcutaneous fat a ccumulation in winter, moreover, may afford slight improvement in phys iological cold insulation during the severe winters as a consequence o f depositing winter fat on the trunk rather than on the periphery. Thu s, the dietary seasonality in Phala is a stress that elicits fluctuati on in fat energy stores but not BMR. (C) 1996 Wiley-Liss, Inc.