Mixed
A 7-day dietary record (7DDR) provides higher relative validity for estimating nutrient intake compared to a single semiquantitative food frequency questionnaire (SFFQ) or averaged 24-hour recalls (ASA24) when validated against urinary and plasma biomarkers.
If you need to know your exact nutrient intake (especially sodium, potassium, or protein) for health reasons, a 7-day food diary is more accurate than a standard food frequency questionnaire or a single day's recall. While FFQs are convenient, they underestimate validity compared to biomarkers. Use a diary if precision matters; use an FFQ only for broad ranking.
In general, relative to biomarkers, averaged ASA24s had lower validity than the SFFQ completed at the end of the data-collection year (SFFQ2); SFFQ2 had slightly lower validity than 1 7DDR; the averaged SFFQs had validity similar to that of 1 7DDR; and the averaged 7DDRs had the highest validity.
Why this rating
Large sample size (n=627), use of objective biomarkers (urinary/plasma), and rigorous statistical deattenuation.
Source
Relative Validity of Nutrient Intakes Assessed by Questionnaire, 24-Hour Recalls, and Diet Records as Compared With Urinary Recovery and Plasma Concentration Biomarkers: Findings for Women
Changzheng Yuan et al. · American Journal of Epidemiology · 2017
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