What is the evidence that probiotics are protective against colorectal cancer?

From the Guidelines

The current evidence suggests that probiotics may have a protective effect against colorectal cancer, although the evidence is not yet conclusive, and more research is needed to fully understand their potential benefits. The most recent study, published in 2023, found that manipulation of the gut microbiome has the potential to influence colorectal cancer (CRC) risk, with a level of agreement of 62% among experts 1. This study also found that stool-based microbial markers have the potential to predict immunotherapy and chemotherapy responses in patients with CRC, with a level of agreement of 92% among experts 1.

Key Findings

• A systematic review of clinical trials showed that probiotic/synbiotic administration improved enteric microbiota by reducing the abundance of potentially harmful bacteria, such as Fusobacterium, Enterococcus, Porphyromonas, Pseudomonas 1.
• Emerging evidence suggests that microbiota modulation can be associated with reduction in CRC-related bacteria and potentially CRC risk 1.
• A randomized, double-blind, placebo-controlled trial involving patients who had colonic polypectomy found that oral treatment with a synbiotic formula led to significant changes in gut microbiota, reduced colorectal proliferation, and improved epithelial barrier function 1.

Recommendations

• Physicians should offer advice on modification of lifestyle habits that could modulate gut microbiota, including low animal protein intake, low fat intake, and high fiber consumption, as well as administration of probiotics 1.
• Regular consumption of probiotics through fermented foods (yogurt, kefir, sauerkraut) or supplements containing multiple strains at doses of at least 1-10 billion CFU daily may be beneficial 1.
• Probiotics should be considered as part of a comprehensive approach to colorectal cancer prevention that includes regular screening, a high-fiber diet, limited red meat consumption, regular exercise, and avoiding smoking and excessive alcohol 1.

Limitations

• The level of evidence of the current recommendations is limited, with a classification of II-2 or III, and more definitive recommendations on the use of probiotics in clinical practice will need more support from data in future large-scale studies 1.
• There exists significant interindividual variation in gut microbiome, influenced by factors such as age, sex, dietary habits, smoking, body mass index, and antibiotic use, which should be taken into account when interpreting the results of studies on probiotics and CRC risk 1.

From the Research

Evidence of Probiotics in Colorectal Cancer Prevention

• The composition of gut microbiota is associated with the development of colorectal cancer (CRC) and other gut dysbiosis, and modulation of gut microbiota by probiotics and prebiotics could positively influence the cross-talk between the immune system and microbiota, preventing inflammation and CRC 2.
• Probiotics supplementation in patients with CRC improved their quality of life, enhanced gut microbiota diversity, reduced postoperative infection complications, and inhibited pro-inflammatory cytokine production 3.
• Probiotic supplementation protects CRC patients from treatment-associated adverse effects, and the beneficial impact of probiotic supplementation depends on several factors such as strain, dosage, duration of the intervention, host physiology, and other food supplements 4.
• Probiotics have properties that make them useful in the management and prevention of colorectal cancer, and can provide a new avenue to reduce the occurrence of this malignancy and enhance patients' quality of life 5.

Mechanisms of Probiotics in Colorectal Cancer Prevention

• Probiotics have antitumor activity with various mechanisms such as nonspecific physiological and immunological mechanisms, alteration of the intestinal microflora, inactivation of cancerogenic compounds, competition with putrefactive and pathogenic microbiota, and improvement of the host's immune response 6.
• Probiotics can reduce the problems associated with chemotherapy and surgery when used synergistically, and can also increase the efficacy of chemotherapeutic medications 5.
• Targeted drug delivery and TRAIL collaboration techniques are other effective and promising methods that involve probiotics 5.

Degree of Protection

• The degree of protection offered by probiotics against colorectal cancer is still being researched, and larger clinical trials of selected or a cocktail of probiotics are needed to confirm the efficacy, dosage, and interactions with chemotherapeutic agents 3.
• The beneficial effects of probiotics in patients with CRC have been observed regardless of the stage of cancer, and there is an opportunity for probiotics to be used in mainstream health care as a therapy in the fight against CRC, especially in early stages 3.