Using the doubly labeled water method (DLW), we determined total energy expenditure (TEE) under free-living conditions in 23 rural Bolivian Aymara (males and females aged 4-65), natives of a small, high-altitude (4000-4100 m), rural agropastoral community in the Andes mountains. In the adults (18-65 y of age), mean TEEs for males and females were 11.1 +/- 1.8 MJ/24 h (range: 9.3-14.1) and 9.8 +/- 0.9 MJ/24 h (8.8-11.3). Non basal energy expenditure expressed as TEE relative to basal energy expenditure (TEE:RMR) and as the difference between TEE and RMR per unit of weight [(TEE-RMR)/wt] showed no significant sex differences. TEE:RMR in the adults (2.00 +/- 0.21) was significantly greater (P < 0.05) than that of adolescents and children (1.67 +/- 0.25), but the mean (TEE-RMR)/wt values were similar in children, adolescents, and adults. Significantly high RMR:FFM values in children and adolescents, reflecting a curvilinear relation of RMR and FFM, have enlarged the differences in TEE:RMR by age groups. When compared with other DLW studies for free-living nonobese adults, the RMR of adult Aymara subjects normalized by the ratio method (RMR:FFM) and by the regression-based method (RMR adjusted with FFM as the covariate) was not significantly different from that observed in subjects living in low altitudes. As compared to FAO/WHO/UNU (1985) recommendations, activity levels were classified as heavy for the adult females and moderate-heavy for the adult males. Energy requirements for maintaining everyday tasks in the Andean people are much higher than expected from the previous studies on food consumption.