Post-diagnosis dietary factors, supplement use and colorectal cancer prognosis: A Global Cancer Update Programme (CUP Global) systematic literature review and meta-analysis

CONCLUSIONS
There was ‘limited-suggestive’ evidence for the associations between post-diagnosis healthy dietary and/or lifestyle patterns, intake of whole grain, or coffee (total, caffeinated, decaffeinated) with lower risk of all-cause mortality, and for the associations between post-diagnosis unhealthy dietary patterns or intake of sugary drinks with higher risk of all-cause mortality. The evidence for other exposure-outcome associations received a ‘limited-no conclusion’ grading.

Conclusions made by the CUP Global independent Expert Committee on Cancer Survivorship and the Expert Panel may contribute towards future formulation of lifestyle guidance/recommendations specific for colorectal cancer survivors. The current evidence is not strong enough for the development of recommendations for cancer survivors following the well-established CUP Global process but a new complementary process, considering evidence which may be more ‘limited’ alongside expert opinion would allow the development of guidance, to provide cancer survivors with sound information based on the best available evidence. To provide conclusions with a higher level of certainty and develop specific lifestyle recommendations, additional evidence is needed from larger, well-designed observational studies in well-characterised populations, with repeated exposure and confounder assessments. Mechanistic studies exploring the biological pathways that underpin potential associations between dietary exposures and colorectal cancer outcomes are crucial to inform recommendations. RCTs,180 that could possibly, evaluate the effects of specific dietary patterns, or coffee183 that have shown survival benefits in this SLR would be informative. MR studies using instrumental exposures to account for confounding and reverse causation153 could be used to clarify the results for circulating 25(OH)D or other biomarkers, and examine the role of diet and gut microbiome on colorectal cancer prognosis.184 Additional studies are also needed in socio-demographically and ethnically diverse survivors, of different cancer stages, and at different phases of the cancer continuum.