In a recent study published in the journal Biochimica et Biophysica Acta - Reviews on Cancer, researchers reviewed existing studies on using fermented food interventions to alter the gut microbiome composition and improve immunotherapy and other cancer treatment outcomes.

Study: Gut microbiome and cancer implications: Potential opportunities for fermented foods. Image Credit: casanisa/Shutterstock.com

Background

A growing body of evidence indicates that the gut microbiota, consisting of various species of bacteria, fungi, viruses, archaea, protozoans, and yeast, plays a significant role in health and disease.

Lower diversity in the gut microbiome has been linked to incidences of colorectal and head and neck cancers, type 1 diabetes, inflammatory bowel disease, celiac disease, and obesity.

Additionally, poor dietary choices and overuse of antibiotics alter the composition and activity of the gut microbiota, which could lead to immune-mediated and inflammatory diseases such as cancer.

The gut microbiome provides an ideal target for preventative and treatment interventions using diets rich in fiber and low in fats, sugars, and processed foods.

Fermented foods, including naturally fermented ones such as kimchi and sauerkraut, and culture-dependent ferments such as kombucha and kefir provide an excellent method to introduce beneficial microbes, including probiotics into the diet and subsequently influence the gut microbiome.

Cancer and the immune system

Immune responses play a pivotal role in cancers, with the loss of control of the immune system resulting in the unchecked proliferation of cancer cells and tumor formation. Immunotherapy aims to strengthen the immune system to recognize and attack the tumor cells.

Immune checkpoint inhibitors are a type of drug used for immunotherapy that prevents checkpoint proteins from attaching to the partner proteins on cancer cells, targeting the cells to be killed by T cells. However, only one-eighth of the patients respond well to immunotherapy.

Studies indicate that the gut microbiome plays an active role in modulating innate and adaptive immune responses. The balance between pathogenic and commensal microbes in the gut is essential in regulating intestinal macrophages through the action of cytokines, lipopolysaccharides, and C-reactive protein.

The abundance of bacterial species belonging to the genera Ruminococcus, Bifidobacterium, Prevotella, and Faecalibacterium have been found to have an inverse relationship with C-reactive protein and interleukin-6, which modulate systemic inflammatory responses.

Fermented food interventions

Microbiome modulation through the diet is the safest, most accessible, and least intrusive method to influence the impact of the gut microbiome on the immune system.

Various dietary patterns and scores, such as the Alternative Mediterranean diet score (aMED) and Dietary Approaches to Stop Hypertension (DASH), have been associated with reduced risk of cancer, cardiovascular disease, and mortality.

The enhancement of immunotherapy through dietary modulations is being studied in various types of cancers, with high-fiber diets showing significant improvements in the probability of progression-free survival among melanoma patients.

However, compared to high-fiber diets, fermented foods significantly increased the alpha diversity in the gut microbiome and reduced inflammation markers.

While not all fermented foods are probiotics, fermented foods are produced through the action of microbes, some of which might be probiotics, such as Lactobacillus, Saccharomyces, Bifidobacteria, and Streptococcus species.

Fermented foods provide various health benefits by increasing the functional and nutritional properties of foods and increasing the bioavailability of nutrients and vitamins.

Additionally, other metabolites formed during the fermentation process, such as exopolysaccharides and lactic acid, are thought to provide a wide range of health benefits. The by-products of fermentation are also believed to have neurogenic and immune-regulatory properties.

Evidence from epidemiological studies has highlighted the health benefits of fermented food consumption. Large cohort studies in the United States have reported a reduction in type 2 diabetes risk, improvements in metabolic parameters, and reduced all-cause mortality risk associated with increased yogurt consumption.

Studies from Asian countries have reported various benefits of kimchi consumption, including reduced risk of atopic dermatitis, reduced blood pressure, a lower risk of diabetes and obesity, and improved metabolic responses.

While probiotics and fermented foods are both comprised of beneficial bacteria, research indicates that fermented foods have a stronger impact on health.

This is potentially due to the buffering effects of food protecting the bacteria during the passage through the digestive tract and the interactions with other food ingredients enhancing the effect of the beneficial microbes.

Conclusions

Overall, the findings suggested that an increased intake of fermented foods could modulate the gut microbiome.

While the evidence for the modulation of immune responses by the gut microbiome is scarce, the authors believe that studies integrating genetic, proteomic, and metabolomic approaches in understanding the role of the gut microbiome in modulating the immune system could help decipher the role of the gut microbiota in cancer treatment outcomes.

Journal reference:

• Crowder, S. et al. (2023) "Gut microbiome and cancer implications: Potential opportunities for fermented foods", Biochimica et Biophysica Acta (BBA) - Reviews on Cancer, 1878(3), p. 188897. doi: 10.1016/j.bbcan.2023.188897. https://www.sciencedirect.com/science/article/abs/pii/S0304419X2300046X?via%3Dihub