Associations Between Ultra-Processed Food (UPF) Consumption and Weight Change and Obesity Risk Among Consumers of Plant-Based Diets: A Systematic Review

Interest in plant-based diets for health promotion continues to grow, emphasizing whole and minimally processed foods. Consistent with broader U.S. trends, plant-based consumers derive many calories from UPFs, whose impact on weight change, overweight, and obesity remains unclear. This review aimed to evaluate the association between UPF consumption and weight change, overweight, and obesity among consumers of plant-based diets. A systematic literature search was performed in Web of Science, PubMed, and Scopus databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol. This review analyzed twelve studies published between 2020 and 2025 involving 206,727 participants aged 18 and older across six countries. There was a mixed association between UPF consumption and weight change, overweight, and obesity among plant-based consumers, with some suggestion that higher diet quality UPFs were inversely or not associated with body weight. Among the 12 studies included, 4 specifically examined the research question, while the rest separately reported baseline UPF intake and weight-related outcomes. The quality of evidence was weak. While the four studies addressing the research question were rated fair to good quality individually, it was not possible to draw definitive conclusions, as the studies were observational and had a high risk of bias. Across the studies, there was also variability in consumption patterns and potential misclassification of plant-based consumers. Further research evaluating the quality of plant-based UPFs and UPF subcategories is warranted, as diet quality appears to be an influencing factor of the association.