Dietary restraint and self-reported meal sizes: diary studies with differentially informed consent

Psychometric methods were used to explore the reliability and criterion val idity of self-reported food intake in studies of dietary restraint. In Stud y 1 the reliabilities over days of daily aggregate intakes and of intakes a t meals at particular times of day were assessed in 7 day food dairies by 2 7 low-BMI females. The sizes of particular meals correlated poorly with eac h other and with the total of all other meals; daily aggregate intakes also had poor reliability (Cronbach's alpha). Individuals meal sizes were consi stent from day to day, with high inter-correlations between meal sizes, hig h correlations between meals at particular times and the sum of the remaind er and high reliabilities. Aggregate intake had moderate criterion validity . Of individual meals, only breakfast achieved criterion validity, but ther e was a significant cubic component in its relationship with restraint. In Study 2, young male and female participants with Various BMIs, completed a food diary on a single day. Again, aggregate daily intake had low reliabili ty. Total intake and breakfast both had criterion validity, dietary restrai nt correlating negatively with total intake and breakfast size in the whole sample and in females, but there were significant quadratic components in the relationships. In contrast, restraint correlated positively with lunch size in the whole sample and in males. The combination of low reliability o f individual meals as estimates of total intake, and the low criterion vali dity of all meals except breakfast, suggests that it may be inappropriate t o study dietary restraint using aggregate self-reported intake measures. (C ) 2000 Academic Press.