Dietary intake measurement using 7 d diet diaries in British men and women in the European Prospective Investigation into Cancer-Norfolk study: a focus on methodological issues

The aim of the present study was to describe the energy, nutrient and crude v. disaggregated food intake measured using 7 d diet diaries (7dDD) for the full baseline Norfolk cohort recruited for the European Prospective Investigation into Cancer (EPIC-Norfolk) study, with emphasis on methodological issues. The first data collection took place between 1993 and 1998 in Norfolk, East Anglia (UK). Of the 30 445 men and women, aged 40-79 years, registered with a general practitioner invited to participate in the study, 25 639 came for a health examination and were asked to complete a 7dDD. Data from diaries with data recorded for at least 1 d were obtained for 99 % members of the cohort; 10 354 (89·8 %) of the men and 12 779 (91·5 %) of the women completed the diet diaries for all 7 d. Mean energy intake (EI) was 9·44 (sd 2·22) MJ/d and 7·15 (sd 1·66) MJ/d, respectively. EI remained approximately stable across the days, but there was apparent under-reporting among the participants, especially among those with BMI >25 kg/m2. Micronutrient density was higher among women than among men. In conclusion, under-reporting is an issue, but not more so than that found in national surveys. How foods were grouped (crude or disaggregated) made a difference to the estimates obtained, and comparison of intakes showed wide limits of agreement. The choice of variables influences estimates obtained from the food group data; while this may not alter the ranking of individuals within studies, this issue may be relevant when comparing absolute food intakes between studies.