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Within- and between-individual variation in energy intakes by low-income Peruvian infants
E G Piwoz1, H Creed de Kanashiro, G Lopez de Romaña
1Department of International Health, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, MD 21205.
Objectives:
(i) To examine the components of variation in infant energy intake. (ii) To calculate the precision of estimates of energy intake from different sources. (iii) To estimate the number of dietary studies required to estimate true energy intake with varying degrees of precision.
Design:
Energy intakes were determined from monthly 12-h observations with test-weighing of breastmilk and all foods consumed. Variance components were evaluated by pooling results of studies performed when infants were 1-4, 5-8 and 9-12 months old.
Setting:
Pueblo Joven Huáscar, 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 and energy from solid foods, and < 1.0 for energy from breast- and non-human milks during the 4-month periods examined. Total energy and energy from breastmilk were estimated to within 13-24% of infants' true intake. Non-breastmilk energy was estimated to within 19-143% of true intake. Four dietary studies per age period are required to estimate total energy and breastmilk energy consumption with 20-30% precision. At least 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 energy intake changes with age and composition of the diet. Thus, the number of dietary studies required to obtain a fixed level of precision differs according to these characteristics.