High daily energy expenditure of Tuvan nomadic pastoralists living in an extreme cold environment

Abstract

Research investigating thermoregulatory energy costs in free-living humans is limited. We determined the total energy expenditure (TEE) of Tuvan pastoralists living in an extreme cold environment and explored the contribution of physical activity and cold-induced thermogenesis. Twelve semi-nomadic pastoralists (47 ± 8 years, 64 ± 8 kg) living under traditional circumstances, in Tuva, south-central Siberia, Russia, were observed during two consecutive 6-day periods in winter. TEE was measured via the doubly labelled water technique. Skin and ambient temperatures, and physical activity were continuously monitored. The outdoor temperature during the observation period was - 27.4 ± 5.4 °C. During the daytime, the participants were exposed to ambient temperatures below 0 °C for 297 ± 131 min/day. The Tuvan pastoralists were more physically active compared to western populations (609 ± 90 min/day of light, moderate, and vigorous physical activity). In addition, TEE was 13.49 ± 1.33 MJ/day (3224 ± 318 kcal/day), which was significantly larger by 17% and 31% than predicted by body mass, and fat-free mass, respectively. Our research suggests the daily cold exposure combined with high levels of physical activity contributed to the elevated TEE. Future research should reconsider the assumption that energy costs due to thermoregulation are negligible in free-living humans.

Figure 1

Example 24-h profiles of environmental temperatures. Indoor temperature was measured inside a yurt. Outdoor temperature was measured outside the same yurt. A participant’s (male, 58 years) ambient temperature was measured with a temperature sensor attached to the outer surface of their clothing. Sampling rate was 5 min.

Figure 2

The relationship between the participant’s ambient temperature and mean skin temperature during the day (07:00–19:00) of the whole period. One subject’s data were excluded due to non-wear of the clothing temperature sensor, therefore n = 11 (8 males and 3 females). Participant numbers 4, 6, and 8 are females.

Figure 3

The relationship between the participant’s body fat % and their mean 24-h skin temperature during period 1 (filled markers) and period 2 (unfilled markers). Circles denote males and squares denote females. The r value is the result of the Pearson correlation.

Figure 4

Measured total energy expenditure (TEE) and TEE predicted by body mass (a) and fat-free mass (b). Predicted TEE high or low/middle HDI refers to the prediction equation created with countries rated as either high, or low/middle on the human development index (HDI).

Figure 5

A map showing the location of Tuva, within Russia, where Mongolia borders Tuva’s south.

Figure 6

Protocol of the field work and measurements involved. DLW indicates consumption of the doubly labelled water. Urine sample collections are denoted by the larger arrows on Days 0, 1, 7, and 13.