Construct validity of the Planetary Health Diet Index relative to global food group-based measures of a healthy diet: a multicountry analysis of 24-hour dietary intake data on the FAO/WHO Global Individual Food Consumption Data Tool.

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 with other global dietary measures remain to be evaluated.

OBJECTIVES

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 with greater risks of diet-related noncommunicable diseases against food group diversity score (FGDS) and Global Diet Quality Score (GDQS), and its positive (GDQS+) and negative (GDQS-) submetrics.

METHODS

Cross-sectional quantitative 24-h recall and food record data from 152,004 nonpregnant females and males (≥15 y) from 45 surveys in 26 countries accessed from the FAO/WHO Global Individual Food Consumption Data Tool were analyzed. 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 ultraprocessed food (UPF)] or indicators of a healthy diet [e.g., ≥400 g/d of fruits 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 income (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 pp, 7.33 pp] in LIC to β: 1.41 pp [95% CI: 1.23 pp, 1.58 pp] in UMIC}, appropriate F&V intakes [relative risk (RR): 2.41 (95% CI: 1.85, 2.49) in UMIC to RR: 1.19 (95% CI: 1.05, 1.34) in LMIC], lower unprocessed red meat [β: -10.0 g/d (95% CI: -11.4 g/d, -8.73 g/d) in LIC to β: -6.86 g/d (95% CI: -7.54 g/d, -6.17 g/d) in UMIC], and lower proportions of energy from UPF [β: -2.47 pp (95% CI: -3.77 pp, -1.18 pp) in LMIC to β: -1.21 pp (95% CI: -2.32 pp, 0.105 pp) in LIC]; however, 1-SD increases in FGDS and GDQS+ outperformed PHDI in predicting measures of nutrient adequacy, particularly MAR [β for FGDS: 11.2 pp (95% CI: 9.13 pp, 13.3 pp) in LIC to β for FGDS: 8.57 pp (95% CI: 8.42 pp, 8.72 pp) in UMIC; β for GDQS+: 9.82 pp (95% CI: 7.26 pp, 12.4 pp) in LMIC to β for GDQS+: 7.18 pp (95% CI: 6.00 pp, 8.36 pp) in HIC] and appropriate F&V intakes [RR for FGDS: 2.78 (95% CI: 2.26, 3.41) in LMIC to RR for FGDS: 1.63 (95% CI: 1.22, 2.19) in HIC; RR for GDQS+: 2.39 (95% CI: 1.89, 2.89) in LMIC to RR for GDQS+: 1.55 (95% CI: 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 the FGDS, often show stronger associations with healthy diet subconstructs, such as nutrient adequacy, and are more feasible for large-scale, routine monitoring of diets.