WITHIN-INDIVIDUAL AND BETWEEN-INDIVIDUAL VARIATION IN ENERGY INTAKES BY LOW-INCOME PERUVIAN INFANTS

Objectives: (i) To examine the components of variation in infant energ y intake. (ii) To calculate the precision of estimates of energy intak e from different sources. (iii) To estimate the number of dietary stud ies required to estimate true energy intake with varying degrees of pr ecision. Design: Energy intakes were determined from monthly 12-h obse rvations with test-weighing of breastmilk and all foods consumed. Vari ance components were evaluated by pooling results of studies performed when infants were 1-4, 5-8 and 9-12 months old. Setting: Pueblo Joven Huascar, a low-income, peri-urban community in Lima, Peru. Subjects: 124 infants who were enrolled at birth and followed monthly. Results: Within-to-between infant variance ratios were >1.0 for total energy an d energy from solid foods, and <1.0 for energy from breast- and non-hu man milks during the 4-month periods examined. Total energy and energy from breastmilk were estimated to within 13-24% of infants' true inta ke. Non-breastmilk energy was estimated to within 19-143% of true inta ke. Four dietary studies per age period are required to estimate total energy and breastmilk energy consumption with 20-30% precision. At le ast 16 studies are required to estimate infants' average energy intake from solid foods from 5-8 months with 30% precision. Conclusions: The degree of precision achieved during assessment of infants' usual ener gy intake changes with age and composition of the diet. Thus, the numb er of dietary studies required to obtain a fixed level of precision di ffers according to these characteristics.