Relative Validity of Food Frequency Questionnaires in Adult Populations: A Systematic Review and Meta-Analysis

Accurate dietary assessment is essential in nutritional research and epidemiology. Food Frequency Questionnaires (FFQs) are widely used to estimate habitual intake; however, their performance may vary according to questionnaire design, administration procedures, and the dietary components being assessed. This systematic review and meta-analysis evaluated the relative validity of FFQs designed to assess overall dietary intake in adults and explored methodological characteristics associated with their performance. A meta-analysis was conducted on studies validating FFQs against reference methods, including 24-h recalls and food records. A comprehensive search of the PubMed, Web of Science, and Scopus databases was conducted for publications from January 2000 to February 1, 2026. Pooled estimates were calculated for correlation coefficients and mean differences for energy and nutrients between FFQs and reference methods. The literature search identified 43 articles that included 8467 participants. Subgroup analyses according to the sample size, administration methods, FFQ items, quality of the studies, and regions were also performed. Overall, FFQs showed moderate-to-good relative validity for most nutrients. Performance was relatively consistent for energy and macronutrients, particularly carbohydrates, whereas greater variability was observed for micronutrients, although some, including magnesium and riboflavin, showed high correlations. Systematic overestimation of certain nutrient intakes was observed, particularly when FFQs were compared with 24HRs. Interviewer-administered FFQs and questionnaires with a greater number of items tended to yield slightly higher correlations, while studies of higher methodological quality also tended to report stronger correlations. These findings support the use of FFQs primarily for ranking individuals according to habitual dietary intake and suggest that administration mode, questionnaire comprehensiveness, and methodological quality should be carefully considered in future FFQ development and validation. Greater caution may be warranted when overall-diet FFQs are used to estimate specific micronutrient intakes.