Planetary Health Diet Index, Plant-Based Dietary Indices, and Cardiovascular Outcomes: A Systematic Review and Meta-Analysis of Observational Studies

Objective: This systematic review and meta-analysis aimed to evaluate the associations of the Planetary Health Diet Index (PHDI) and plant-based dietary indices with cardiovascular outcomes and to quantitatively synthesize prospective cohort evidence examining PHDI adherence in relation to incident total cardiovascular disease (CVD), coronary heart disease (CHD), and stroke. Methods: PubMed/MEDLINE, Scopus, Embase, and Google Scholar were searched from database inception through 31 December 2025 for observational studies evaluating PHDI or plant-based dietary indices in relation to cardiovascular outcomes. Eight studies met the eligibility criteria. Four prospective cohort studies assessing PHDI and reporting sufficiently comparable highest-versus-lowest adherence contrasts were included in random-effects meta-analyses using the DerSimonian–Laird method. Separate pooled hazard ratios (HRs) with 95% confidence intervals (CIs) were calculated for total CVD, CHD/MI, and stroke. Statistical heterogeneity was evaluated using Cochran's Q and I². Four additional studies evaluating structurally different plant-based indices or non-prospective outcomes were synthesized narratively. Risk of bias was assessed using ROBINS-E, and robustness was examined through leave-one-out and risk-of-bias sensitivity analyses. The review was registered with PROSPERO (CRD420261327062). Results: Eight studies were included, of which four prospective PHDI cohorts contributed to the quantitative synthesis. Higher versus lower PHDI adherence was associated with lower incidence of total CVD (HR 0.85, 95% CI 0.81–0.89; k=4; I²=0%), CHD/MI (HR 0.84, 95% CI 0.80–0.89; k=3; I²=0%), and stroke (HR 0.84, 95% CI 0.78–0.91; k=3; I²=0%). The direction and magnitude of the pooled associations remained generally stable in sensitivity analyses. Narrative findings for other plant-based dietary indices were more heterogeneous. Some studies suggested lower cardiovascular risk with healthful and minimally processed plant-based dietary patterns and higher risk with unhealthful or ultra-processed plant-based patterns, whereas other conventional plant-based indices showed no significant association with total CVD. Publication bias could not be reliably assessed because fewer than five studies contributed to each pooled outcome. Conclusion: Higher PHDI adherence was consistently associated with lower incidence of total CVD, CHD/MI, and stroke across the available prospective cohorts. Findings for other plant-based dietary indices were less consistent and appeared to vary according to dietary quality and degree of food processing.