Post-diagnostic ultra-processed food exposure in gastrointestinal cancers: scoping review with narrative synthesis and clinical implications

Background: Modifiable lifestyle factors, including diet quality, are strongly associated with the incidence of gastrointestinal cancers. However, the impact of ultra-processed food (UPF) consumption after cancer diagnosis remains poorly understood, with scarce and fragmented evidence. In particular, the role of post-diagnostic UPF exposure in shaping survival outcomes and disease progression has not been systematically explored. Methods: We conducted a scoping review with narrative synthesis of the available literature on post-diagnostic UPF consumption and clinical outcomes in gastrointestinal cancers. Eligible studies included adult patients with gastrointestinal malignancies, assessment of dietary exposure after diagnosis, and outcomes such as overall survival, cancer-specific mortality, recurrence, progression, and treatment-related outcomes. Results: Direct evidence was extremely limited. The only available prospective study in colorectal cancer survivors showed that higher post-diagnostic UPF intake was not associated with overall or cancer-specific mortality but was associated with increased cardiovascular mortality, highlighting the relevance of competing risks in cancer survivorship. Furthermore, specific UPF subgroups showed adverse associations with colorectal cancer-specific mortality. Supportive studies suggested that dietary quality may deteriorate after treatment, with increasing UPF consumption over time. Mechanistic evidence supports a biologically plausible link between UPF exposure, metabolic dysfunction, chronic inflammation, microbiota alterations, and survivorship outcomes. Conclusions: Despite the increasing burden of gastrointestinal cancers and the widespread consumption of ultra-processed foods, post-diagnostic UPF exposure remains largely overlooked in oncologic research. Direct evidence is currently limited and mainly restricted to colorectal cancer survivors, where higher UPF intake has been associated with cardiovascular mortality but not consistently with cancer-specific outcomes. These findings, together with biological plausibility from mechanistic studies, support the need for prospective post-diagnostic cohorts and intervention trials integrating standardized dietary assessment into gastrointestinal cancer survivorship research.