Construct validity of the Planetary Health Diet Index relative to global food group-based measures of a healthy diet: A multi-country analysis of 24-hour dietary intake data on the FAO/WHO Global Individual Food Consumption Data Tool.
TL;DR
PHDI may serve as a robust, dual purpose measure for monitoring adherence to diets that are both sustainable and healthy in contexts with regular quantitative dietary intake assessments and low burdens of diet-related undernutrition, however, simpler food group-based measures such as FGDS often show stronger associations with healthy diet sub-constructs such as nutrient adequacy, and are more feasible for large-scale, routine monitoring of diets.
Abstract
Background
The Planetary Health Diet Index (PHDI) was developed as a measure of adherence to the Planetary Health Diet proposed by the EAT-Lancet Commissions, however, its construct validity for accurately reflecting a healthy diet as compared to other global dietary measures remains to be evaluated.
Objective
The construct validity of PHDI was assessed by comparing the strength of its associations with reference metrics of nutrient adequacy and moderation of foods associated greater risks of diet-related non-communicable diseases against food group diversity score (FGDS) and Global Diet Quality Score (GDQS) and its Positive (GDQS+) and Negative (GDQS-) sub-metrics.
Methods
Cross-sectional quantitative 24-hour recall and food record data from 152,004 non-pregnant females and males (≥15 years) from 45 surveys in 26 countries accessed from the FAO/WHO Global Individual Food Consumption Data Tool were analysed. Multilevel linear and modified Poisson regression models quantified associations between PHDI, FGDS, GDQS+, and GDQS- with reference measures [e.g., mean adequacy ratio (MAR), % energy from ultra-processed food (UPF)] or indicators of a healthy diet [e.g., ≥400 g/day of fruit and vegetables (F&V)], respectively.
Results
Adherence to PHDI was highest in low-income (LIC) and lower-middle income countries (LMIC), and lowest in upper-middle (UMIC) and high income countries (HIC). One-SD increments in PHDI were associated with higher MAR (β: 5.49 percentage points (pp); 95% confidence interval (CI): 3,65, 7.33 in LIC to 1.41 (1.23, 1.58) in UMIC), appropriate F&V intakes (relative risk (RR): 2.41 (1.85, 2.49) in UMIC to 1.19 (1.05, 1.34) in LMIC), lower unprocessed red meat (β: -10.0 g/day (-11.4, -8.73) in LIC to -6.86 (-7.54, -6.17) in UMIC), and lower proportions of energy from UPF (β: -2.47 pp (-3.77, -1.18) in LMIC to -1.21 (-2.32, 0.105) in LIC), however, one-SD increases in FGDS and GDQS+ outperformed PHDI in predicting measures of nutrient adequacy, particularly MAR (β for FGDS: 11.2 pp (9.13, 13.3) in LIC to 8.57 (8.42, 8.72) in UMIC; β for GDQS+: 9.82 (7.26, 12.4) in LMIC to 7.18 (6.00, 8.36) in HIC) and appropriate F&V intakes (RR for FGDS: 2.78 (2.26, 3.41) in LMIC to 1.63 (1.22, 2.19) in HIC; RR for GDQS+: 2.39 (1.89, 2.89) in LMIC to 1.55 (1.16, 1.96) in LIC).
Conclusions
PHDI may serve as a robust, dual purpose measure for monitoring adherence to diets that are both sustainable and healthy in contexts with regular quantitative dietary intake assessments and low burdens of diet-related undernutrition, however, simpler food group-based measures such as FGDS often show stronger associations with healthy diet sub-constructs such as nutrient adequacy, and are more feasible for large-scale, routine monitoring of diets.