Varying levels of food energy self-reporting are associated with between-group, but not within-subject, differences in food intake

Energy intakes reported in diet diaries are frequently significantly below the energy requirements for a weight-stable individual. To investigate the impact of low energy reporting on between-group comparisons and within-subject analyses of eating behavior, we examined the baseline 7-d food-intake diaries submitted by 365 male and 564 female free-living normal adult humans. Participants were separated into 5 different groups, based upon their levels of energy reporting relative to their predicted basal metabolic rate: EI:BMRest = 0-0-99, 1.0-1.199, 1.2-1.399, 1.3-1.599, and >= 1.6. Between-group analysis revealed significant inverse relations among reporting level and body weight, BMI, cognitive restraint, positive relations with intake, meal size, and meal frequency. On the other hand, within-subject analyses suggested that, regardless of the level of energy reporting, equivalent relations are found among the amounts eaten in meals and the presence of other people, palatability, hunger, satiety, dietary energy density, contents of the stomach, time since the last meal, and time of day and correlations between daily intake and intake on subsequent days. The results suggest that comparing the intakes reported in diet diaries by different groups may be confounded by group differences in reporting levels. In contrast, the results clearly support the conclusion that diet diary data are suitable for assessing the relations between variables assessed within subjects irrespective of the level of reporting of energy intake.