Higher Total Energy Expenditure Contributes to Growth Faltering in Breast-Fed Infants Living in Rural Mexico

Abstract

To investigate the energy requirements of infants living under unfavorable environmental conditions in rural Mexico, we measured the total energy expenditure (TEE) of 40 Otomi infants at approximately 4 or approximately 6 mo of age. Total energy expenditure was estimated by the doubly labeled water method: 100 mg 2H2O/kg and 250 mg 18O/kg were administered orally, after which urine was collected serially for 7 or 10 d. Isotopic enrichment of urine samples was analyzed by gas-isotope-ratio mass spectrometry. Weight and length were measured monthly from birth to 6 mo. Fat free mass was estimated from 18O dilution spaces. Total energy expenditures (mean +/- SD) were 310 +/- 58 and 318 +/- 29 kJ.kg-1 x d-1 at approximately 4 and approximately 6 mo, respectively. Total energy expenditure was higher than that previously observed for breast-fed infants reared under more protected environments (268 +/- 29 kJ.kg-1 x d-1). Weight, length and weight gain were 5.9 +/- 0.8 kg, 60 +/- 2 cm and 2.9 +/- 2.4 g.kg-1 x d-1 at 4.25 mo and 7.1 +/- 0.8 kg, 65 +/- 2 cm and 1.0 +/- 1.2 g.kg-1 x d-1 at 6.27 mo. Growth faltering was evident at 6 mo by clinically significant declines in growth velocities and National Center for Health Statistics Z-scores. Body fat of the Otomi infants averaged 21 +/- 6 and 18 +/- 5 g/100 g at approximately 4 and approximately 6 mo, respectively. Higher rates of TEE narrowed the margin of energy available for growth and thereby contributed to growth faltering in the Otomi infants.