Can the Gut Microbiome Switch Cancer Off?

​How the trillions of microbes inside us may hold one of the most critical control levers in the cancer journey

When I started my cancer journey, I saw the tumor as an enemy in my body, something we fought with chemo, surgery, and radiation. Over time, I came to understand something deeper: the real battleground isn’t just my tumor or blood; it’s my gut. The countless microbes there are not just passive observers; they influence inflammation, immune response, metabolism, and even the effectiveness of my treatments.

What if cancer isn’t just about rogue cells, but also about an imbalance in the system? What if restoring a healthy microbial community gives us an advantage? In this post, I will explain why the gut microbiome matters in cancer, the science behind it, and what you can do.

1. The Gut-Cancer Connection: From Metabolism to Immunity

Our gut does more than digest food; it acts as a metabolic and immune organ. The microbial community living there, known as the gut microbiome, affects nutrient absorption, immune cell training, hormone signaling, and even gene expression in other parts of the body.

Clinical studies have shown that microbes in the gastrointestinal tract and elsewhere can influence cancer development, tumor progression, treatment response, and side effects. For instance, a review titled “The Microbiome and Cancer: A Translational Science Review” concluded:

"Clinical and preclinical evidence suggests that microbes in the gastrointestinal tract may affect cancer development, metastasis, treatment response, and adverse effects."
https://jamanetwork.com/journals/jama/fullarticle/2833859

Another major review states:

“The gut microbiome plays a crucial role in cancer development and progression by influencing the host immune system and metabolism.”
https://www.nature.com/collections/gahafacddj

Here are some ways the microbiome links to cancer:

• Immune modulation: Beneficial microbes help train our immune cells, including T-cells, NK cells, and antigen-presenting cells, to recognise threats and maintain tolerance. Dysbiosis, or a loss of microbial diversity, disrupts this balance, leading to chronic inflammation or immune suppression.
• Metabolic signaling: Microbes produce metabolites, such as short-chain fatty acids (SCFAs), bile acids, and indoles, that circulate in the body and directly affect cell signaling, gene expression, and immune-cell behavior.
• Barrier function and inflammation: A healthy gut lining prevents microbes from leaking into the bloodstream, which can cause systemic inflammation. Chronic inflammation is a well-known promoter of cancer.
• Direct genotoxicity: Some gut bacteria release toxins, such as colibactin from certain E. coli, that damage DNA and may trigger tumor formation.

https://en.wikipedia.org/wiki/Colibactin

In summary, the gut microbiome goes beyond aiding digestion; it interacts with our immune, metabolic, and cancer systems. While going through treatment, I realised that maintaining gut health became a vital part of my survival strategy.

2. The Gut as a Drug Response Modulator

Recent findings show that the gut microbiome can impact treatment outcomes. Bacteria not only live in us; they influence how our therapies work.

Several studies involving patients receiving immune checkpoint inhibitors (ICIs) found that higher gut microbial diversity and certain bacterial strains, like Akkermansia muciniphila (this is the one I use: Amazon Link) and Faecalibacterium prausnitzii, correlate with better treatment responses.
See: https://pubmed.ncbi.nlm.nih.gov/40629403/

A 2023 review states that dietary changes, probiotic/prebiotic strategies, and fecal microbiota transplantation (FMT) are being investigated to improve ICI effectiveness by altering the gut microbiome.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10537950/

In practical terms:

• Patients who had taken broad-spectrum antibiotics before immunotherapy often faced worse survival outcomes due to compromised microbiome diversity.
• Trials indicate that increasing dietary fiber intake, which supports beneficial gut bacteria, is linked to improved responses to immunotherapy.

If the gut microbiome acts as a “co-therapist” in cancer treatment, then rebuilding its strength is essential.

3. Microbial Metabolites That Fight (or Feed) Tumors

Let’s examine the chemicals produced by gut microbes and their roles in cancer.

1. Short-Chain Fatty Acids (SCFAs)
   When fiber is fermented in the colon, bacteria produce SCFAs like acetate, propionate, and butyrate. Butyrate, in particular, is beneficial: it nourishes colon cells, maintains gut barrier integrity, supports immune function, and may slow tumor growth.
   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10170910/

   In one study, higher levels of SCFA-producing bacteria were linked to better immunotherapy results.
   https://pubmed.ncbi.nlm.nih.gov/40629403/

2. Secondary Bile Acids and Indoles
   Some gut bacteria convert bile acids or amino acids into compounds that can promote cancer. For instance, certain secondary bile acids and hydrogen sulfide may cause inflammation and DNA damage.
   https://www.frontiersin.org/articles/10.3389/fmicb.2024.1287077/full

   On the other hand, indole derivatives from tryptophan metabolism support gut immunity and anti-tumor actions.

3. Genotoxic Metabolites
   As mentioned, colibactin from specific E. coli strains can damage DNA and has been associated with early-onset colorectal cancer.
   https://www.nature.com/articles/s41575-022-00664-3

   In other words, microbial chemicals are significant. They affect pathways related to metabolism, DNA damage, immune function, and barrier integrity, all of which are relevant in cancer. If your gut microbiome produces the right metabolites and suppresses the harmful ones, you're likely to have better resilience against tumor development and growth.

4. How the Microbiome Communicates With Tumors

The communication between gut bacteria and tumor cells is intricate but becoming more evident.

You can visualise it like this: your gut microbiome → microbial metabolites plus immune cell training → systemic inflammation and immunity → tumor microenvironment (TME) → tumor behavior and response to treatment.

Here are some key points:

• Gut-derived metabolites influence signaling pathways in immune cells that infiltrate tumors (for example, NF-κB, mTOR, and AMPK pathways).
  https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-024-05709-3
• Dysbiosis, characterised by reduced diversity and dominance of inflammatory bacteria, is linked to worse outcomes in several cancers, especially colorectal cancer.
  https://pmc.ncbi.nlm.nih.gov/articles/PMC7541789/
• Microorganisms found within tumor tissue, known as the “tumor microbiome,” also impact how immune cells behave in that area.
  https://pmc.ncbi.nlm.nih.gov/articles/PMC10802201/
• As someone navigating this journey, I see the microbiome as a hidden force: if it’s weak, your immune system struggles to respond effectively; if it’s robust, your body stands a better chance.

5. Rebuilding a Cancer-Resistant Microbiome

What can you do? Knowing that the gut is important is one thing; acting on it is another.

• Diet
  Focus on high-fiber, plant-oriented diets. These provide food for SCFA-producing bacteria.
  “Higher fiber consumption was consistently linked to better treatment responses in patients undergoing immunotherapy.”
  https://pubmed.ncbi.nlm.nih.gov/40629403/

  Limit ultra-processed foods, high sugar, and low-fiber diets that reduce microbial diversity. https://www.bmj.com/content/376/bmj-2021-068575

• Probiotics, Prebiotics, and Fermented Foods
  Though research on commercial probiotics in cancer is still ongoing, fermented foods like kefir, sauerkraut, and live-culture yogurt help maintain microbial diversity.

  Specific bacteria, such as Akkermansia muciniphila and Faecalibacterium prausnitzii, are associated with better treatment outcomes, although it is still under investigation whether supplementing with them is effective. https://www.sciencedirect.com/science/article/pii/S1043661823001846

  Prebiotics, such as resistant starch, inulin, and certain fibers, nourish beneficial microbes.

  FMT is being studied in clinical oncology as a potential reset tool. https://www.nature.com/articles/s41591-021-01220-2

• Avoid Gut Insults
  Steer clear of unnecessary antibiotics, as they can wipe out microbial diversity.
  “Antibiotics taken before immunotherapy have been linked to poorer outcomes.” https://pmc.ncbi.nlm.nih.gov/articles/PMC10093606/

  Limit excessive alcohol intake, aim for good sleep, reduce stress, and avoid overuse of NSAIDs since all these factors affect gut-microbe balance.

• Lifestyle
  Regular exercise, sufficient sleep, and managing stress all benefit gut health indirectly through hormone regulation, nerve communication, and gut movement.

  For me, rebuilding my gut microbiome has felt empowering. I focus on real food, enjoy fermented snacks, avoid processed bars, and treat my gut as a vital part of my defense.

6. Personal Reflection: My Microbiome Strategy

During treatment, I dealt with gut-related issues: antibiotics, mucositis, poor appetite, and high sugar cravings. I realised that while I could confront the tumor directly, I also had to protect my gut health.

I took several steps:

• Daily consumption of fermented foods like kale and sauerkraut.
• Following a “plant-forward, fiber-rich vegetarian diet” with a degree of ketogenic and low-processed foods.
• Steering clear of packaged “health” bars, as they often lack real fiber and contain added emulsifiers.
• Carefully reading ingredient labels for unfamiliar additives, which can disrupt gut ecology.
• Monitoring bowel health, gut recovery, and pain rather than ignoring it.

As a result, I noticed improved digestion, smoother recovery from treatment, fewer gut infections, and a better mood. Whilst I can’t prove this changed my tumor’s behavior, I feel stronger, more resilient, and better able to recover.

7. The Future: Personalised Microbiome Medicine in Oncology

We are entering a new age in cancer treatment: not just “eat more fiber,” but targeted microbiome interventions. Studies now use AI and other advanced tools to identify which microbial profiles respond best to various therapies.

A 2025 review discusses how the gut microbiome is becoming a focus in cancer immunotherapy. https://www.nature.com/articles/s41573-025-01211-7

AI-based modeling at major cancer centers is linking specific microbial patterns to immune cell activation rates.
https://www.massgeneralbrigham.org/en/about/newsroom/articles/enhancing-cancer-immunotherapy-by-looking-at-the-gut-microbiome

Trials are underway studying the combination of dietary fiber, microbiome shifts, and checkpoint inhibitors, with results expected in the coming years.
https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-025-06586-0

In conclusion, while the microbiome won’t replace surgery, chemo, or radiation, it may enhance their effectiveness, reduce side effects, and strengthen long-term resilience.

8. Key Takeaways

Your gut microbiome plays a significant role in cancer. It affects metabolism, immunity, and barrier function, all of which influence cancer risk and treatment response.

Microbial metabolites, such as SCFAs and toxins, serve as chemical signals affecting tumor behavior.

Diet, fermentation, lifestyle choices, and avoiding gut harm can build microbial resilience.

In cancer treatment, your gut microbiome may affect how well therapies work, especially immunotherapy.

Take practical steps: adopt a high-fiber diet, consume fermented foods, avoid unwarranted antibiotics, ensure good sleep and movement, and check food labels for processed ingredients.

In the future, personalised microbiome medicine will be an integral part of cancer care.

My journey involves strengthening my body while confronting the tumor. For me, gaining control is crucial.

​References

1. Understanding the role of the gut microbiome in gastrointestinal … https://pmc.ncbi.nlm.nih.gov/articles/PMC9903080/
2. The Microbiome and Cancer: A Translational Science Review https://jamanetwork.com/journals/jama/fullarticle/2833859
3. The gut microbiome as a target in cancer immunotherapy https://www.nature.com/articles/s41573-025-01211-7
4. Gut microbiome changes and cancer immunotherapy outcomes https://pubmed.ncbi.nlm.nih.gov/40629403/
5. Role of gut microbiome in cancer immunotherapy: from predictive … https://ehoonline.biomedcentral.com/articles/10.1186/s40164-023-00442-x
6. Gut microbiota and its therapeutic implications in tumor … https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1287077/full
7. A Review of Gut Microbiota-Derived Metabolites in Tumor … https://pmc.ncbi.nlm.nih.gov/articles/PMC10214247/
8. Studies linking microbiome to cancer: A mini-review on contemporary … https://www.sciencedirect.com/science/article/pii/S2950194625000470
9. The gut microbiome and cancer response to immune checkpoint … https://www.jci.org/articles/view/184321
10. The gut microbiome and cancer: from tumorigenesis to therapy https://pubmed.ncbi.nlm.nih.gov/40329009/
11. Microbiome and cancer: from mechanistic implications in disease … https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2024.1373504/full
12. Facts and Hopes for Gut Microbiota Interventions in Cancer … https://pubmed.ncbi.nlm.nih.gov/35748749/
13. The human microbiome and cancer: a diagnostic and therapeutic … https://pmc.ncbi.nlm.nih.gov/articles/PMC10376920/
14. Influence of the gut microbiota on immune cell interactions and … https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-024-05709-3
15. Targeting the Gut Microbiome to Improve Immunotherapy Outcomes … https://pmc.ncbi.nlm.nih.gov/articles/PMC11369881/