Comparison of diet measures from a food-frequency questionnaire with measures from repeated 24-hour dietary recalls. The Norwegian Women and Cancer Study.

Objective: To compare diet measures from a food-frequency questionnaire (FFQ) with measures from 24-hour dietary recalls (24HDRs).

Design: The participants answered an FFQ after completing four, repeated 24HDRs during a year.

Setting: Norway, nationwide.

Subjects: Of 500 women randomly selected from The Norwegian Women and Cancer Study (the Norwegian arm of the European Prospective Investigation into Cancer and Nutrition), 286 agreed to participate and 238 completed the study.

Results: On the group level, the FFQ overestimated absolute intake in seven and underestimated intake in six of 21 food groups. Intakes of energy, fat, added sugar and alcohol were lower in the FFQ than in the 24HDRs, whereas intake of fibre was higher. Spearman's rank correlation coefficient ranged from 0.13 (desserts) to 0.82 (coffee) for foods, and from 0.25 (beta-carotene) to 0.67 (alcohol) for nutrients. Three per cent of the observations on nutrient intake fell in the opposite quintile when classified according to the FFQ as compared with the 24HDR. The median calibration coefficient, calculated by regression of the 24HDR data on the FFQ data, was 0.57 for foods and 0.38 for nutrients.

Conclusions: The FFQ's ability to rank subjects was good for foods eaten frequently and fairly good for macronutrients in terms of energy percentages. Weaker ranking abilities were seen for foods eaten infrequently and for some micronutrients. The results underline the necessity of performing measurement error corrections.