The association between overall, healthy, and unhealthy plant-based diet indexes and risk of all-cause and cause-specific mortality: a systematic review and dose-response meta-analysis of prospective cohort studies

Background: recent dietary guidelines recommend a diet that mainly includes plant-based foods and a moderate amount of animal products. Therefore, we hypothesized that plant-based diet indices (overall plant-based diet index (oPDI), healthy plant-based diet index (hPDI), and unhealthy plant-based diet index (uPDI)) might be associated with risk of all-cause and cause-specific mortality. Methods: a systematic review was conducted using PubMed, Web of Science, Scopus, and Embase databases until December 2024. Meta-analysis was performed utilizing random-effects models to calculate relative risk (RR) with the corresponding 95% confidence intervals (95% CIs). Results: from 436 initial records, 25 prospective studies met the inclusion criteria. The findings of our study indicated a modest inverse association between the adherence to oPDI and risk of all-cause mortality (RR [95% CI]: 0.89 [0.83-0.94]; n = 15 studies) as well as mortality related to cardiovascular diseases, chronic heart disease, and total cancer. Also, adherence to hPDI was found to reduce risk of all-cause (RR [95% CI]: 0.86 [0.82-0.90]; n = 21 studies), cardiovascular disease, chronic heart disease, total-cancer, and prostate cancer mortality, whereas uPDI was associated with higher risk of all-cause (RR [95% CI]: 1.20 [1.13-1.27]; n = 19 studies), cardiovascular disease, chronic heart disease, and total-cancer mortality. Our dose-response meta-analysis showed a monotonic inverse association between adherence to oPDI and hPDI and a positive linear association between adherence to uPDI and risk of all-cause mortality. Conclusion: our findings highlight the importance of evaluating the quality of plant-based foods as either healthy or unhealthy in relation to the risk of all-cause and cause-specific mortality.