Ultra-Processed Foods and Breast Cancer: Epidemiology, Mechanisms, and Prognostic Implications.

Ultra-processed foods (UPFs) have become a dominant component of modern diets and are increasingly implicated in metabolic disorders, inflammation, and cancer risk. Emerging epidemiologic evidence suggests that high UPF intake is associated with increased breast cancer incidence and may influence prognosis and survivorship outcomes, although heterogeneity remains across populations and tumor subtypes, and specific UPF exposures. Given the rising incidence of early-onset breast cancer, which coincides with increasing UPF consumption and prolonged early-life exposure, understanding the potential role of UPF exposure in younger populations represents an emerging public health priority. This review synthesizes current findings on UPF consumption, specific UPF subgroups, food additives, and related exposures in relation to breast cancer risk, including early-onset and other subgroup-specific associations, life course exposure, mechanistic pathways, and prognostic implications. We highlight evidence linking UPFs to metabolic dysregulation, endocrine disruption, microbiome perturbation, oxidative stress, and carcinogen exposure, and discuss the relevance of metabolomics, lipidomics, and other multi-omics approaches in elucidating causal pathways. Finally, we outline research priorities aimed at refining exposure assessment, strengthening causal inference and informing cancer prevention and survivorship strategies.