Associations between plant-based dietary patterns and risks of type 2 diabetes, cardiovascular disease, cancer, and mortality – a systematic review and meta-analysis

BACKGROUND: Plant-based dietary patterns are gaining more attention due to their potential in reducing the risk of developing major chronic diseases, including type 2 diabetes (T2D), cardiovascular disease (CVD), cancer, and mortality, while an up-to-date comprehensive quantitative review is lacking. This study aimed to summarize the existing prospective observational evidence on associations between adherence to plant-based dietary patterns and chronic disease outcomes. METHODS: We conducted a systematic review and meta-analysis of evidence across prospective observational studies. The data sources used were PubMed and MEDLINE, Embase, Web of Science, and screening of references. We included all prospective observational studies that evaluated the association between adherence to plant-based dietary patterns and incidence of T2D, CVD, cancer, and mortality among adults (≥ 18 years). RESULTS: A total of 76 publications were identified, including 2,230,443 participants with 60,718 cases of incident T2D, 157,335 CVD cases, 57,759 cancer cases, and 174,435 deaths. An inverse association was observed between higher adherence to a plant-based dietary pattern and risks of T2D (RR, 0.82 [95% CI: 0.77–0.86]), CVD (0.90 [0.85–0.94]), cancer (0.88 [0.84–0.92]), and all-cause mortality (0.84 [0.78–0.92]) with moderate to high heterogeneity across studies (I(2) ranged: 30.2–95.4%). The inverse associations with T2D, CVD and cancer were strengthened when healthy plant-based foods, such as vegetables, fruits, whole grains, and legumes, were emphasized in the definition of plant-based dietary patterns (T2D: 0.79 [0.72–0.87]; CVD: 0.85 [0.80–0.92]; cancer: 0.86 [0.80–0.92]; I(2) ranged: 53.1–84.1%). Association for mortality was largely similar when the analyses were restricted to healthy plant-based diets (0.86 [0.80–0.92], I(2) = 91.9%). In contrast, unhealthy plant-based diets were positively associated with these disease outcomes. Among four studies that examined changes in dietary patterns, increased adherence to plant-based dietary patterns was associated with a significantly reduced risk of T2D (0.83 [0.71–0.96]; I(2) = 71.5%) and a marginally lower risk of mortality (0.95 [0.91–1.00]; I(2) = 0%). CONCLUSIONS: Better adherence to plant-based dietary patterns, especially those emphasizing healthy plant-based foods, is beneficial for lowering the risks of major chronic conditions, including T2D, CVD, cancer, as well as premature deaths. REGISTRATION OF REVIEW PROTOCOL: This review was registered at the PROSPERO International Prospective Register of Systematic Reviews (https://www.crd.york.ac.uk/PROSPERO/) with the registration number CRD42022290202. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12937-023-00877-2.