Background: Information on within- and between-individual variation in energy and nutrient intake is critical for precisely estimating usual dietary intake; however, data from Japanese populations are limited.
Methods: We used dietary records to examine within- and between-individual variation by age and sex in the intake of energy and 31 selected nutrients among Japanese adults. We also calculated the group size required to estimate mean intake for a group and number of days required both to rank individuals within a group and to assess an individual’s usual intake, all with appropriate arbitrary precision. A group of Japanese women (younger: 30–49 years, n = 58; older: 50–69 years, n = 63) and men (younger: 30–49 years, n = 54; older: 50–76 years, n = 67) completed dietary records for 4 nonconsecutive days in each season (16 days in total).
Results: Coefficients of within-individual variation and between-individual variation were generally larger in the younger group than in the older group and in men as compared with women. The group size required to estimate a group’s mean intake, and number of days required to assess an individual’s usual intake, were generally larger for the younger group and for men. In general, a longer period was required to rank women and older adults.
Conclusions: In a group of Japanese adults, coefficients of within-individual variation and between-individual variation, which were used to estimate the group size and number of records required for adequate dietary assessment, differed by age, sex, and nutrient.
2013 Japan Epidemiological Association. This is an open access article distributed under the terms of Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.