Plant-Based Diets, Ultra-Processed Foods, and Risks of Mortality and Major Chronic Diseases: A Prospective Cohort Study.

Background: Higher-quality plant-based diets (PBDs) are associated with lower risks of mortality and chronic disease, but whether ultra-processed food (UPF) content affects these associations remains unclear. We examined whether UPF content influences the relationship between plant-based dietary patterns and risks of mortality and major chronic diseases, accounting for nutrient quality. Methods: This prospective cohort study included 124,836 UK Biobank participants aged 40-70 years (recruited 2006-2010). Dietary intake was assessed using the Oxford WebQ 24-h recall. Four modified Plant-Based Diet Indices (PDIs) were derived to distinguish healthy (hPDI) and unhealthy (uPDI) patterns with high- and low-UPF content, using the Nova classification and a Modified Nutrient Quality Index (mNQI). Participants were followed for 8.3-10.5 years for all-cause mortality and incident T2DM, CVD, and cancer. Multivariable Cox models estimated hazard ratios (HRs) and 95% confidence intervals (CIs). Findings: Among 124,836 participants (mean [SD] age 56.2 [7.8] years; 55.8% women), there were 5780 deaths, 3420 T2DM cases, 6078 CVD cases, and 9437 cancer cases. Higher adherence to healthy plant-based diets-whether high- or low-UPF-was associated with 8-28% lower risk of all-cause mortality [HR Interpretation: Adherence to healthful PBDs is associated with more favourable health outcomes irrespective of UPF content, suggesting that overall PBD quality may be more important than processing level for chronic disease prevention. Funding: This research was supported by Research Ireland, Northern Ireland's Department of Agriculture, Environment and Rural Affairs (DAERA), UK Research and Innovation (UKRI) via the International Science Partnerships Fund (ISPF) under Grant number 22/CC/11147 at the Co-Centre for Sustainable Food Systems.