Plant-Based Diets and Mental and Neurocognitive Health Outcomes: A Systematic Review With Meta-Analysis.

Context: Emerging evidence suggests the quality of plant-based diets may play a pivotal role in the primary prevention of certain nonfatal diseases. However, its impact on mental and neurocognitive health conditions remains to be elucidated.

Objective: To synthesize the available evidence on the cross-sectional and prospective associations of adherence to overall, healthy, and unhealthy plant-based diets with mental and neurocognitive health outcomes in the general adult population (aged ≥18 years).

Data Sources: The PubMed, Scopus, and Web of Science databases were searched from inception through March 13, 2024. Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Meta-analyses of Observational Studies in Epidemiology guidelines were followed for this study.

Data Extraction: Random-effects meta-analyses were performed using the Sidik-Jonkman estimator. Pooled odds ratios (ORs) and risk ratios (RRs) with their 95% CIs were estimated for cross-sectional and prospective associations between the highest (vs lowest) adherence to plant-based diets and the likelihood of adverse mental and neurocognitive health outcomes (ie, anxiety, depression, psychological distress, cognitive decline, and dementia).

Data Analyses: A total of 23 studies involving 709 703 adults (mean age range: 31.4-102.3 years; 52.8% female) were included. The highest (vs lowest) adherence to healthy plant-based diets was significantly associated with a lower likelihood of anxiety (OR = 0.67; 95% CI, 0.46-0.96), depression (OR = 0.74; 95% CI, 0.57-0.96), and psychological distress (OR = 0.51; 95% CI, 0.39-0.65) in cross-sectional studies and with a lower risk of cognitive decline (RR = 0.74; 95% CI, 0.64-0.85), dementia (RR = 0.85; 95% CI, 0.76-0.96), and depression (RR = 0.77; 95% CI, 0.67-0.88) in cohort studies. Conversely, greater adherence to unhealthy plant-based diets was significantly associated with an increased likelihood of anxiety and depression. When the data were subjected to a standardized effect size correction (Hedges g) to mitigate potential biases, the results remained consistent.

Conclusion: High-quality plant-based diets could play an important role in the primary prevention of mental and neurocognitive health conditions.

Systematic Review Registration: PROSPERO registration no. CRD42024524053.