Comparison of single questions and brief questionnaire with a longer validated food frequency questionnaire to assess adequate fruit and vegetable intake

Objective: The aim of this study was to determine if a single question (SQ) for fruit and a SQ or 5-item questionnaire for vegetable consumption (VFQ) could replace a longer Food Frequency Questionnaire (FFQ) to screen for inadequate versus adequate intakes in populations. Research Methods and Procedures: Participants (109) completed three test screeners: fruit SQ, vegetable SQ, and a 5-item VFQ followed by the reference 74-item FFQ (the DQESv2) including 13 fruit and 25 vegetable items. The 5-item VFQ asked about intake of salad vegetables, cooked vegetables, white potato, legumes and vegetable juice. The screeners were compared with the reference (DQESv2 FFQ) for sensitivity, specificity, positive and negative predictive powers (PPV, NPV) to detect intakes of 2 or more serves fruit and 3 or more serves vegetables. Relative validity was examined using Bland Altman statistics. Results: The fruit SQ showed PPV of 56% and NPV of 83%. For the vegetable SQ the PPV was 30% and NPV 89%. For the 5-item VFQ the PPV was 39% and NPV 85%. Bland Altman plots and linear regression equations showed that while the screener showed good agreement for fruit, (unstandardised b1 coefficient = 0.04) for vegetable intake the difference between methods increased at higher intake levels, (unstandardised b1 coefficients = -0.3 for the SQ, b1 = -0.6 for 5-itemVFQ). Conclusion: The SQ for fruit and 5-item VFQ are suitable replacements for longer FFQ to detect inadequate intake and assess population mean but not individual intakes.