RELATIVE VALIDITY OF SHORT QUESTIONNAIRES TO ASSESS MEDITERRANEAN DIET OR LOW-FAT DIET ADHERENCE

Background: Short diet questionnaires can quickly identify dietary habits with minimal burden for users but they require validation for use in specific populations. Objective: To assess relative validity against a food frequency questionnaire (FFQ) of two short questionnaires to assess a Mediterranean diet and a low-fat diet, respectively, among organ transplant recipients as a part of a pilot study. Design: Cross-sectional validation study. Setting: Heart or lung transplant recipients completed two short dietary questionnaires and a full semi-quantitative FFQ as the reference methods, on 3 separate days. Participants: Sixteen heart (n=8) or lung (n=8) transplant recipients aged 16 years or more, at least 6-months post-transplant and clinically stable patients in Manchester, UK. Measurements: Two short dietary questionnaires to assess their Mediterranean diet and low-fat diet and a semi-quantitative FFQ. Relative validity was assessed by comparing the scores derived from each short questionnaire with that of the FFQ. Agreement was assessed using the limits of agreement (LOA), and the agreement was expressed as a ratio of the score from the short dietary to the FFQ score with a ratio of 1.00 indicating perfect agreement. The agreement was formally tested by the two one-sided t-test procedure. Results: The mean agreement was 0.99 (95% LOA 0.60–1.38) for the Mediterranean and 1.04 (95% LOA 0.42–1.64) for the low-fat diet. The two one-sided t-test procedure showed the short questionnaires and the reference method were equivalent (Mediterranean diet overall p=0.004; low-fat diet overall p<0.001). Conclusions: Dietary habits to measure Mediterranean diet and a low-fat diet by short dietary questionnaires and full FFQ were comparable among organ transplant recipients.