The European Prospective Investigation into Cancer and Nutrition, the largest study of diet and cancer ever conducted, followed over 519,000 participants across 10 European countries. It found that people with the highest dietary fibre intake had a 40 percent lower risk of colorectal cancer compared to those with the lowest intake. The World Cancer Research Fund's meta-analysis of 25 prospective cohort studies confirmed a 10 percent reduction in colorectal cancer risk for each additional 10 grams of dietary fibre per day.
Mechanisms of Protection
Dietary fibre reduces colorectal cancer risk through multiple complementary mechanisms. Insoluble fibre increases stool bulk and reduces transit time, decreasing the contact time between potential carcinogens in the colon content and the colonic epithelium. Soluble fibre fermentation produces butyrate, which promotes apoptosis of pre-cancerous cells and inhibits the growth of cancer cells while sparing normal colonic cells. Fibre also reduces secondary bile acid concentrations in the colon by binding bile acids in the gut lumen.
The Role of the Microbiome
A fibre-rich diet supports a diverse microbiome with high levels of butyrate-producing bacteria including Faecalibacterium prausnitzii and Roseburia intestinalis. These bacteria maintain colonic epithelial health through butyrate production, reduce colonic pH to levels unfavourable for pathogenic bacterial growth, and modulate local immune surveillance in ways that reduce cancer risk. The mechanistic connection between dietary fibre, the gut microbiome, and colorectal cancer protection is one of the most well-characterised diet-cancer pathways in nutritional science.