The effect of under-reporting of energy intake on dietary patterns and on the associations between dietary patterns and self-reported chronic disease in women aged 50-69 years.

The aim of this cross-sectional study was to investigate whether under-reporting of energy intake affects derived dietary patterns and the association between dietary patterns and self-reported chronic disease. Diets of 6204 women aged 50-69 years participating in the Norwegian Breast Cancer Screening Program were assessed using a 253-item FFQ. We identified dietary patterns using principal component analysis. According to the revised Goldberg cut-off method, women with a ratio of reported energy intake:estimated BMR<1·10 were classified as low energy reporters (n 1133, 18 %). We examined the associations between dietary patterns and self-reported chronic diseases by log-binomial regression, and the results are presented as prevalence ratios (PR) and CI. 'Prudent', 'Western' and 'Continental' dietary patterns were identified among all reporters and plausible reporters. The PR expressing the associations between the 'Western' and 'Prudent' dietary pattern scores and self-reported chronic diseases were consistently highest among plausible reporters except for joint/muscle/skeletal disorders. The largest difference in PR among plausible v. all reporters was found for the association between the 'Prudent' pattern and diabetes (PR for highest v. lowest tertile: PRall reporters 2·16; 95 % CI 1·50, 3·13; P trend<0·001; PRplausible reporters 2·86; 95 % CI 1·81, 4·51; P trend<0·001). In conclusion, our results suggest that under-reporting can result in systematic error that can affect the association between dietary pattern and disease. In studies of dietary patterns, investigators ought to consider reporting effect estimates both for all individuals and for plausible reporters.