Dietary fibre supplementation enhances radiotherapy tumour control and alleviates intestinal radiation toxicity

Abstract Background Non-toxic approaches to enhance radiotherapy outcomes are beneficial, particularly in ageing populations. We investigated the efficacy of high-fibre diets combined with irradiation in C57BL/6 mice bearing bladder cancer flank allografts. Result Psyllium plus inulin significantly decreased tumour size and delayed tumour growth following irradiation compared to 0.2% cellulose and raised intratumoural CD8 + cells. Post-irradiation, tumour control positively correlated with Lachnospiraceae family abundance. Psyllium plus resistant starch radiosensitised the tumours, positively correlating with Bacteroides genus abundance. Although local immunity was suppressed, psyllium plus resistant starch increased caecal isoferulic acid levels, associated with a favourable response. Both diets mitigated the acute radiation injury caused by 14 Gy. All high fibre diets increased caecal short-chain fatty acid levels. Similar gut microbiota profiles in cancer patients and low-fibre diet mice indicates scope for testing dietary fibre supplements in human intervention studies. Conclusion These supplements may be useful in combinations with radiotherapy in patients with pelvic malignancy.