Total energy expenditure and physical activity level of lactating Mesoamerindians

Energy-sparing mechanisms may be elicited to meet increased energy requirements imposed by lactation on women who reside in poor, rural communities in developing countries. The objectives of this study were to measure total energy expenditure and its components, basal and activity energy expenditure, and to investigate their relationships with lactation performance in a total of 40 rural Mesoamerindians stratified according to postpartum body mass index. Total energy expenditure and fat-free mass were measured by the doubly labeled water method, and basal metabolic rate was determined by indirect calorimetry at 3 and 6 mo postpartum. Physical activity level was taken as the ratio of total energy expenditure to basal metabolic rate. Milk energy output, which is not included in total energy expenditure, was computed from 24-h milk intake (test-weighing) and energy concentration of milk (bomb calorimetry). Anthropometric measurements revealed negligible mobilization of tissue stores. Mean (+/- SD) total energy expenditures were 8912 +/- 1296 kJ/d and 9253 +/- 1298 kJ/d for the lower and higher body mass index groups, respectively. Adjusted for fat-free mass, total energy expenditure was higher in the lower body mass index group (P = 0.05). Adjusted for fat-free mass, basal metabolic rate did not differ between groups. Physical activity level was significantly higher in the lower body mass index group (P = 0.03). Lactation performance did not differ between groups and was not associated with total energy expenditure or its components. Despite the maintenance of energy balance and heightened energy requirements of lactation, energy-sparing mechanisms were not evident in these lactating Mesoamerindians.