The role of plant-based dietary patterns in reducing COVID-19 risk and/or severity in adults: A systematic review and meta-analysis of observational studies

Background & aims: Plant-based dietary patterns (PBDs) might protect against COVID-19 risk and reduce severity of infection. This systematic review with meta-analysis aimed to examine the association between PBDs and risk of COVID-19 infection, hospitalization, intensive care unit (ICU) admission, and/or mortality, in adults.

Methods: Pubmed, Embase, CINAHL and Web of Science were searched for observational studies, published in English up to 3rd April 2023, comparing the highest with the lowest adherence to a specific PBD. Data were screened, extracted, and risk of bias assessed using the Newcastle-Ottawa Quality Assessment Scale, by independent reviewers.

Results: Seven studies (one cross-sectional, three case-control, and three prospective cohort), reporting on 649,315 participants, were eligible. Across them, there were 8512 events of COVID-19 infection (six studies), and 206 events of COVID-19 hospitalization (four studies), in addition to one study reporting on a composite hospitalization outcome (740 events). The pooled analysis showed that PBDs are associated with a 59% (odds ratio (OR) = 0.41, 95% confidence intervals (CI) 0.23-0.59; two studies) and 18% (OR = 0.82, 95% CI 0.78-0.85; three studies) reduction in COVID-19 infection risk in case-control and cohort studies, respectively. The pooled analysis of one case-control and two cohort studies showed an inverse association between high adherence to a PBD and risk of COVID-19 hospitalization (OR = 0.38, 95% CI 0.04-0.72).

Conclusion: Findings suggest a protective role of PBDs against the risk of COVID-19 infection and severity. More studies are needed to establish the association between PBDs and risk of ICU admission and mortality due to COVID-19.