Day-to-day variation in energy and nutrient intake: evidence of individuality in eating behaviour?

A study of within-subject variation in the reported food intakes and food selections of 29 adults participating in the Beltsville One-Year Dietary Intake Study suggests that individuals possess characteristics levels of day-to-day variation in intake. Application of Bartlett's test of homogeneity of variance indicated heterogeneity of within-subject variance in energy intake and in selected nutrients controlled for energy. Comparisons of estimates of within-subject variation derived from a split sample of days revealed the relative stability of individuals' magnitudes of day-to-day variation in energy and nutrient intake over time. For some nutrient variables, a large proportion of the observed heterogeneity in within-subject variation could be explained by a linear relationship between subjects' standard deviations and their mean intake levels. However, heterogeneity persisted when subjects' coefficients of variation were compared, suggesting that mean intake differences are insufficient to explain the observed differences in subjects' levels of day-to-day variation. The magnitude of observed variation in an individual's food intake and food selection from one day to the next appears to be a meaningful descriptor of that individual's intake behaviour.