Variability of nutrient intake over a 3-day period.

This study was designed to assess the magnitude of variation in nutrient intake of individuals over a 3-day period. It is based on an analysis of 3-day food intake records of 21,867 participants in the Nationwide Food Consumption Study (NFCS), 1977-78. Results from a subsample of 7,287 subjects showed a significantly greater variation from the median than from the mean for protein, vitamin A, and iron. Fewer than 30% of the respondents had intakes of any of the 11 nutrients studied within +/- 15% of the mean on all days. For all nutrients except energy and magnesium, less than 50% of the respondents had intakes within +/- 25% of the mean. Variability in intake was greatest for vitamins A and C, with 85% and 82% of respondents, respectively, having low and high daily intakes deviating by more than 25% from the mean. These findings document that 1-day food records alone are of limited value in assessing nutrient adequacy of an individual and quantify the magnitude of the variation over a 3-day period. The more adequate the mean nutrient intake, the less variability in intake from day to day. Similarly, the more consistent the meal pattern, the less the variability in intake.