Populations in transition to a Western lifestyle display increased incidences of obesity, type 2 diabetes, and other chronic diseases; the mechanisms responsible for these changes, however, remain incompletely understood. Although reduced physical activity has been implicated, few studies have accurately quantified energy expenditure in subsistence populations. The aim of the study was to examine the relation of total energy expenditure (TEE) and activity [physical activity level (PAL), activity energy expenditure (AEE), and weight-adjusted AEE (AEE/kg)] with body composition and lifestyle in the Yakut (Sakha), an indigenous high-latitude Siberian group. We measured TEE using doubly labeled water and resting metabolic rate using indirect calorimetry in 28 young adults (14 women and 14 men) from Berdygestiakh, Russia. The men had higher TEE (12,983 compared with 9620 kJ/d; P < 0.01), AEE (5248 compared with 3203 kJ/d; P < 0.05), AEE/kg (72.7 compared with 48.8 kJ . kg(-1) . d(-1); P < 0.05), and PAL (1.7 compared with 1.5; P = 0.09) than did the women, although this may reflect, in part, body size and composition differences. Overweight men and women had modestly higher TEEs than did lean participants; when adjusted for body size, activity levels were not significantly different between the groups. Persons with more traditional lifestyles had higher TEEs and PALs than did persons with more modernized lifestyles; this difference correlated with differences in participation in subsistence activities. Activity levels in the Yakut were lower than those in other subsistence groups, especially the women, and were not significantly different from those in persons in industrialized nations. Persons who participated in more subsistence activities and consumed fewer market foods had significantly higher activity levels.