(P11-002-24) Reproducibility and Validity of Planetary Health Diet Index Derived From Food-Frequency Questionnaires

Objectives: We developed a Planetary Health Diet Index (PHDI) which contains 15 components (range 0-140) to quantify adherence to the EAT-Lancet reference diet. This study aimed to evaluate the reproducibility and validity of the PHDI derived from food frequency questionnaires (FFQ).

Methods: We included 652 men from the Men’s Lifestyle Validation Study (2011-2013) and 742 women from the Women’s Lifestyle Validation Study (2010-2012) who were free of cancer, and major cardiovascular/neurologic disease. Participants completed two 152-item FFQs (at baseline and 1 year later), two weighed 7-d dietary records (7DDRs) and provided two blood samples 6 months apart between the two FFQs. We used rank intraclass correlation coefficients (ICCs) to assess the reproducibility of the FFQs and Spearman rank correlation coefficients to assess the validity of FFQ-derived PHDI with those from the average of two 7DDRs. Also, we calculated the correlations between PHDI and dietary plasma biomarkers including fatty acids, folate, carotenoids, retinol, and α-and γ -tocopherol. Furthermore, we estimated the associations between the calibrated PHDI and mortality and environmental impacts in three prospective cohorts of U.S. men and women using the calibration and bootstrap method.

Results: The FFQ-derived PHDI demonstrated high reproducibility (energy-adjusted ICCs: 0.73-0.78) and validity (energy-adjusted, deattenuated r_s = 0.73–0.77) in both men and women. We consistently observed expected correlations between FFQ-derived PHDI with plasma fatty acids, including long-chain n3(ω-3) and trans fatty acids, most carotenoids, and γ -tocopherol (r_s > 0.2). After calibrating the FFQ-derived PHDI to two-weighed-7DDR-PHDI. After we calibrated the FFQ-derived PHDI to the PHDI assessed by weighed diet records, the observed associations between PHDI and mortality were slightly strengthened, and between PHDI and environmental impacts were stronger in both men and women.

Conclusions: Our analysis documents the validity of the FFQ for evaluating adherence to the PHDI. Correlations between the PHDI assessed by FFQ and circulating biomarkers support its biological relevance.

Funding Sources: This work was supported by research grants from the National Institutes of Health.