Short-Chain Fatty Acids and Colorectal Cancer: A Systematic Review and Integrative Bayesian Meta-Analysis of...

Objective: Existing studies on short-chain fatty acids (SCFAs) and colorectal cancer (CRC) yield contradictory conclusions and are limited to single ethnic groups or sample types. This study aimed to (1) quantify associations between total SCFAs/subtypes (acetate, propionate, butyrate) and CRC/advanced colorectal adenoma (A-CRA) risks; (2) identify modifiers (ethnicity, sample type, intervention); and (3) clarify SCFA-gut microbiota interaction mechanisms via integrative Bayesian meta-analysis and multi-ancestry data integration. Methods: We systematically searched PubMed, Embase, Cochrane Library, and Web of Science (inception to September 2025) using keywords: "Short-chain fatty acids", "SCFAs", "Colorectal cancer", "CRC", "Gut microbiota", "Dietary fiber", and "High-amylose maize starch butyrate". Eligible studies included 14 peer-reviewed original studies (7 observational, cohort/case-control/cross-sectional; 7 RCTs) covering Europeans, Asians, and African Americans. Inclusion criteria: Quantitative SCFA data (total/≥3 subtypes), clear ethnic grouping, reported CRC/A-CRA risks or intervention outcomes. Exclusion criteria: Reviews, animal/in vitro studies, incomplete data, low-quality studies (Newcastle-Ottawa Scale [NOS] <6 for observational; high Cochrane risk for RCTs), or limited populations (single gender/rare genetics). A Bayesian hierarchical random-effects model quantified effect sizes (Odds Ratio [OR]/Mean Difference [MD], 95% credible intervals [CrI]), with heterogeneity analyzed via multi-ancestry stratification, intervention efficacy, and microbiota interaction analyses (Preferred Reporting Items for Systematic Reviews and Meta-Analyses [PRISMA] 2020; International Prospective Register of Systematic Reviews [PROSPERO]: CRD420251157250). Results: Total SCFAs were negatively associated with CRC (OR = 0.78, 95% CrI: 0.65-0.92) and A-CRA (OR = 0.72, 95% CrI: 0.59-0.87), with butyrate showing the strongest protective effect (CRC: OR = 0.63, 95% CrI: 0.51-0.77). Ethnic heterogeneity was significant: Europeans had the strongest protection (OR = 0.71), Asians had weaker protection (OR = 0.86), and African Americans had the lowest fecal SCFA levels and the highest CRC risk. Fecal SCFAs showed a stronger CRC association than serum/plasma SCFAs (OR = 0.73 vs. 0.85). High-Amylose Maize Starch Butyrate (HAMSB) outperformed traditional fiber in increasing fecal butyrate (MD = 4.2 mmol/L vs. 2.8 mmol/L), and high butyrate-producing bacteria (Clostridium, Roseburia) enhanced SCFA protection (OR = 0.52 in high-abundance groups). Conclusions: SCFAs (especially butyrate) protect against CRC and precancerous lesions, with effects modulated by ethnicity, sample type, and gut microbiota. High-Amylose Maize Starch Butyrate is a priority intervention for high-risk populations (e.g., familial adenomatous polyposis, FAP), and differentiated strategies are needed: 25-30 g/d dietary fiber for Europeans, 20-25 g/d for Asians, and probiotics (Clostridium) for African Americans. Future Perspectives: Expand data on underrepresented groups (African Americans, Latinos), unify SCFA detection methods, and conduct long-term RCTs to validate intervention efficacy and "genetics-microbiota-metabolism" crosstalk-critical for CRC precision prevention.