High Intra/Interindividual Variance Ratios for Energy and Nutrient Intakes of Pregnant Women in Rural Malawi Show That Many Days Are Required to Estimate Usual Intake

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Abstract
Conventional wisdom suggests that because there is less variety in food intake, fewer days may be needed to capture “usual intake” of individuals in developing countries, but it is also known that intakes may vary considerably across seasons. Because few studies have examined the sources of variation in nutrient intake in subsistence communities, where food availability also may limit day-to-day food choices, our objective was to examine intraindividual and interindividual variability in energy and nutrient intakes in pregnant subsistence farmers in Africa. From 1988 through 1991, we collected a total of 1061 diet days (mean = 6; range; 2–12 d/woman), using the direct food weighing method, from 184 pregnant women in a farming community west of Lilongwe City, Malawi. Two or four consecutive days were collected for each of several visits during the 2nd and 3rd trimesters. Variance ratios were calculated as the error variance/variance across individuals. We found major seasonal differences in energy and nutrient intakes with greater intakes in the harvest than in the preharvest seasons. Adjustment for season and stage of pregnancy did not reduce variance ratios. To estimate true individual intakes within an error range of ± 20% required 8–23 d for energy, protein, carbohydrates and fiber; and 95–213 d for micronutrients. Thus, despite limited dietary diversity, large within-person variation in nutrient intake demonstrated that more, rather than fewer days of dietary intake were required to correctly identify usual intake in subsistence farmers compared with previous reports for urbanized or Western populations.