We examined within-person and between-person differences in self-selected diets of free-living individuals when they choose to consume or not to consume plain water. We used 2-days of dietary data from the NHANES 2005-2012 for this study. For within-person analyses, we compared recalls of respondents who reported water in one of the two available recalls (n = 1875 men and 1479 women). For between-person analysis, we compared dietary recalls of respondents who reported water in two, one of two, or zero of two recalls (n = 8632 men and 8907 women). The outcomes examined included reported intakes of 24-h energy from foods, beverages, and dietary and eating pattern attributes. We used covariate-adjusted regression methods for both types of analyses. For within-person analyses, the regression models included separate person-level fixed effects. Relative to the water day, on the no-water day, amount of beverages and energy contribution of beverages were significantly higher in both men (106 kcal) and women (43 kcal) (P ≤ 0.002). However, the water and the no-water days did not differ in 24-h energy intake, or the amount and energy from reported foods (P > 0.05). Energy density of foods, servings of fruits or vegetables and eating patterns did not differ between the water and the no-water day in both men and women (P > 0.05). For between-person analysis, however, intakes of energy and energy density of foods were higher, but density of sodium, potassium, and magnesium were lower among those who reported no water in both recalls. Overall, beverages partially substituted for plain water on the no-water day but qualitative dietary characteristics and eating patterns, which may relate to habitual food intake and personal preferences, were not appreciably different within individuals.
