Fibre, microbes and radiotherapy: unravelling the gut's impact on radiotherapy in cancer.

The gut microbiome plays an integral role in many physiological functions, including immunity, metabolism, maintenance of membrane integrity and protection against pathogenic bacteria. Conversely, adverse changes in the gut microbiome-termed dysbiosis-have been linked to many diseases, including cancer. Dysbiosis can result from a range of endogenous and exogenous factors. Diet is one of the most important modulators of the gut microbiome; the indirect benefits of modulating the microbiome through diet interventions are beginning to be used in many disease settings. Beneficial microbes (commensals) can modulate the local and systemic immune environment through the production of metabolites, such as short-chain fatty acids (SCFAs). Commensal bacteria ferment dietary fibre to produce SCFAs, and increasing dietary fibre intake has been shown to both increase SCFA production in the colon and affect immune responses. Recent studies have shown that dietary fibre can increase tumour responses to immunotherapy and chemotherapy, but data on the effect of increased fibre and changes in the microbiome on radiotherapy are limited. In this article, we review the current evidence regarding dietary fibre interventions and modulation of the gut microbiome in improving outcomes in patients receiving pelvic radiotherapy.