Mechanism
Dietary fiber (cereals, fruits, vegetables, legumes) undergoes anaerobic fermentation by colonic bacteria, producing short-chain fatty acids — primarily butyrate, propionate, and acetate. Butyrate is the preferred energy source for colonocytes and exerts direct anti-tumor effects: it inhibits histone deacetylase (HDAC) activity, induces cell cycle arrest and apoptosis in transformed cells, and suppresses pro-inflammatory NF-kB signaling.
Rationale
Colorectal cancer develops in an environment of depleted SCFA producers, reduced butyrate availability, and compromised epithelial barrier function. Dietary fiber applies two-sided ecological engineering (Primitive 5) — it feeds beneficial SCFA-producing taxa (Faecalibacterium, Roseburia, Eubacterium rectale) while the butyrate produced directly inhibits tumor cell proliferation.
Evidence Status
- Epidemiological: Multiple meta-analyses confirm inverse association between fiber intake and CRC risk (~10% reduction per 10g/day).
- Mechanistic: Butyrate's HDAC inhibition and apoptosis induction in CRC cells are well-established.
- Animal model: High-fiber diets reduce tumor burden in APC-min mouse models.
- Clinical: Validated at the epidemiological level; interventional RCTs for fiber in CRC prevention show mixed results (likely due to intervention duration).
Open Questions
- Optimal fiber type (cereal vs. fruit vs. resistant starch) for maximal CRC protection.
- Whether fiber intervention can reduce recurrence in CRC survivors.
- Minimum duration of high-fiber diet needed for protective microbiome shifts.