Effects of combined dietary fiber and probiotic supplementation on gut microbiota, immune function, and clinical outcomes in patients with advanced colorectal cancer: a retrospective cohort study.

[OBJECTIVE] To evaluate the efficacy of a combined intervention of dietary fiber and probiotics on gut microbiota composition, systemic immune response, nutritional status, and long-term prognosis in patients with advanced colorectal cancer (CRC) undergoing conventional therapy.

[METHODS] This retrospective cohort study included 80 patients with advanced CRC and diagnosed malnutrition, treated between May and December 2022. Patients were divided into a control group (n = 40), which received standard nutritional support, and an observation group (n = 40), which received standard support supplemented with a daily formulation of dietary fiber and multi-strain probiotics for 12 weeks. Primary endpoints included changes in immune markers (IgA, IgG, CD4+/CD8+ ratio) and gut microbiota composition (alpha and beta diversity, and specific genera abundance via 16S rRNA sequencing). Secondary endpoints were nutritional status (body mass index [BMI], Patient-Generated Subjective Global Assessment [PG-SGA]), quality of life (WHOQOL-100), and 3-year survival outcomes.

[RESULTS] Baseline characteristics were well-matched between groups (p > 0.05). After 12 weeks, the observation group exhibited significantly higher levels of IgA (0.95 ± 0.24 vs. 0.78 ± 0.15 g/L), IgG (9.34 ± 1.35 vs. 8.05 ± 1.16 g/L), and an improved CD4+/CD8+ ratio (2.18 ± 0.20 vs. 1.56 ± 0.15) compared to the control group (all p < 0.01). The intervention led to superior improvements in BMI (+ 2.83 kg/m vs. + 0.77 kg/m), PG-SGA scores (4.67 ± 0.44 vs. 6.14 ± 0.50), and WHOQOL-100 scores (98.27 ± 7.38 vs. 72.35 ± 6.79) (all p < 0.001). Microbiota analysis revealed a significant increase in the Shannon diversity index and distinct clustering in beta diversity, alongside enriched relative abundance of Lactobacillus and Bifidobacterium in the observation group (p < 0.001). Importantly, the observation group demonstrated a higher 3-year survival rate (83.5% vs. 67.4%, p = 0.001) and a numerically lower incidence of overall complications (7.5% vs. 17.5%, p = 0.176), including a reduction in grade ≥ 3 diarrhea and mucositis, although these differences did not reach statistical significance due to sample size limitations.

[CONCLUSION] In patients with advanced CRC, supplementing conventional therapy with dietary fiber and probiotics effectively modulates the gut microbiota, enhances systemic immune function, improves nutritional status and quality of life, and is associated with better long-term survival. These findings advocate for the integration of gut microbiota-targeted nutritional strategies into standard oncological care.