Adherence
Food-frequency questionnaires (FFQs) systematically overestimate the intake of dairy products and vegetables while underestimating cereal and meat intake compared to 7-day diet diaries, with the magnitude of error varying by sex.
If you are tracking your diet for health optimization, a food diary (recording what you eat in real-time) will give you a more accurate picture of your actual intake than trying to estimate your average habits over a year. Be aware that self-reported long-term habits often skew high for healthy foods (veg/dairy) and low for processed/meat items. For precise nutrient tracking, use a diary; for broad lifestyle categorization, an FFQ-style review is sufficient.
The questionnaire overestimated dairy products and vegetables in both men and women when compared with intakes derived from the diary, but underestimated cereal and meat intake in men.
Why this rating
Based on a large nested validation study (n=300) comparing FFQ against gold-standard 7-day diaries and biomarkers (urine/plasma), with statistically significant p-values.
Source
Nutritional methods in the European Prospective Investigation of Cancer in Norfolk
Sheila Bingham et al. · Public Health Nutrition · 2001
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