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This week, research from Johns Hopkins University School of Medicine, published in Nature, has clarified how a common gut bacterium can drive colon cancer in animal models. It’s a significant step forward, closing a gap that’s been open since 2009. But the conversation in the mainstream press often stops short of what matters most: what this means for you, and what you can do now.
The headlines focus on the bacterial mechanism. The more important question is: what can we do now? Before there’s a new drug, and before a diagnosis is even on the table.
That is where Integrative Medicine has always worked, and it’s where we think this conversation deserves more attention.
What the Research Actually Found
The bacterium at the centre of this study is enterotoxigenic B. fragilis (ETBF). It’s been detected in roughly 20% of healthy adults in certain study populations1, usually without causing harm. However, it has been implicated in intestinal issues like Inflammatory Bowel Disease2, and a particular toxin-producing strain has been linked to colon cancer for over fifteen years. The key question has been: what does this toxin actually do?
This new research provides an answer. The toxin binds to a receptor protein in the colon wall called claudin-4. That interaction allows it to breach the gut’s protective lining, triggering inflammation and, over time, creating conditions in which tumours can develop. When researchers blocked the claudin-4 receptor with a decoy protein, the toxin couldn’t attach. In animal models, the colon’s barrier stayed intact.
“Understanding how bacterial toxins work can open doors to new approaches for detection and therapy for associated diseases, including diarrhea, colorectal cancer and bloodstream infections.” — Professor Cynthia Sears, lead author, as reported by the Daily Mail
The next step is to see if these results hold true in humans. This is important science; however, the usual framing (scientists discover a mechanism, then a drug intervention follows) often leaves people with no clear next step. I want to offer a different perspective and something more practical.
The Part that Often Gets Missed: Oral Health & Fusobacterium Nucleatum
While work on B. fragilis is a significant step toward understanding the role of the microbiome in colorectal cancer development, it is not the only bacterium implicated. In fact, some of the most compelling research in recent years has focused on Fusobacterium nucleatum, a bacterium that typically resides in the mouth and is a known contributor to periodontal (gum) disease.3
Research has demonstrated that F. nucleatum can travel from the oral cavity to the colon, either through the bloodstream via bleeding gums or by surviving the acidic environment of the stomach when swallowed.4 Once in the colon, specific subtypes of this bacterium (e.g. the Fna C2 clade) have been found in approximately 50% of human colorectal tumours.5 The Fusobacterium nucleatum promotes cancer growth in two key ways: a protein called FadA latches onto colon cells and triggers abnormal growth 6, while the bacteria simultaneously suppresses the immune system, making it harder for the body to detect and destroy cancer cells.7
Meta-analyses have found that individuals with periodontal disease face a significantly elevated risk of colorectal cancer, with estimates ranging from 21%8 to 70%9 depending on study design and population. This highlights a crucial, often-overlooked reality: The microbiome does not just exist in the gut; gut health and systemic inflammation are also deeply connected to oral hygiene. At the centre of both stories, though, is the same vulnerability, the gut lining itself, and how permeable it is to what passes through.
Why Integrative Medicine Has Been Here for a While
Claudin-4 isn’t an obscure molecule. It’s part of the tight junction system (the network of proteins that holds the cells of the gut lining together and determines how permeable that lining is to what passes through).
Intestinal permeability is the term used to describe the state of that barrier, and it’s something Functional Medicine has been investigating and addressing for years. Gastrointestinal Mapping (which includes assessing the prevalence of B. fragilis bacteria) is also a cornerstone of Functional testing. That is to say, the importance of intestinal permeability isn’t a fringe idea. It’s a measurable, clinically relevant marker that correlates with chronic inflammation, immune dysregulation, and, increasingly, systemic disease10.
At The Forbes Clinic, our position on this research is straightforward. The mechanism identified by researchers operates within a gut environment shaped by diet, lifestyle, oral health, antibiotic history, and microbial diversity. These are factors we can influence. They were modifiable before this study, and they still are. Waiting for a claudin-4 blocker to reach clinical trials isn’t the only option. The smarter move is an approach to healthcare that focuses on optimising gut health and the oral microbiome, and on addressing factors that contribute to disease development before treatment is necessary.
Toxicity, Inflammation, and the Pattern Beneath the Symptoms
At the heart of Integrative and Functional Medicine is a perspective that many people with complex or chronic health concerns recognise: chronic low-grade inflammation isn’t just a symptom, it’s a driver. The factors that fuel it (microbial imbalance, environmental toxins, compromised barriers, chronic stress, poor diet and more) are often upstream of a diagnosis by years.
The bacterial toxin story is a clear example. A toxin breaches the gut lining. The body responds with inflammation. If that inflammation persists, it creates an environment where cellular dysfunction can occur.
Bowel cancer is the dramatic end of a spectrum. However, the same underlying mechanism shows up in many chronic conditions. The gut, and the inflammatory load it contributes to or helps contain, is a factor in countless chronic health issues, including autoimmune disease, chronic fatigue, hormonal dysregulation, and neurological symptoms, to name a few.
This is why, when someone comes to me with symptoms that haven’t been fully explained, I don’t start with the symptom. I start by asking: what’s driving the inflammatory pattern? In that investigation, the gut is almost always part of the picture.
The Bigger Picture
Colorectal cancer claims more than 17,000 lives in the UK each year.11 It is also increasing among younger adults; while the absolute number of cases in young people remains low, the relative incidence among adults in their twenties has nearly tripled since the early 1990s.12
No single factor fully explains this rise. Obesity, ultra-processed diets, microplastics, and declining physical activity have all been implicated. Today's younger generations have also grown up in an era of widespread antibiotic use. Every course changes the gut microbiome, sometimes temporarily, sometimes more significantly, with research showing that antibiotic use in childhood is associated with disruption to the microbiome that can last for extended periods.13 A less diverse microbiome is a more hospitable environment for pro-inflammatory bacteria.
This isn’t a reason to avoid antibiotics when they’re needed. They save lives, of course. It is, however, a reason to prioritise health interventions that optimise immune health, thereby reducing the need for antibiotic intervention. As well as prioritising an intentional approach to gut microbiome recovery after antibiotics, and taking seriously the evidence that diet and lifestyle shape which bacteria thrive in the gut over time.
What We See in Practice
Many people who come to The Forbes Clinic with persistent gut symptoms, such as bloating, irregular bowel function, diarrhoea, IBS-type symptoms, and low-grade abdominal discomfort, have already been told their tests are normal.
Normal on standard NHS tests. However, those tests typically look for markers of active disease or significant pathology, not for subtle imbalances that may precede it.
What those tests usually don’t capture is the state of the microbiome, indicators of intestinal barrier function, or the dietary, psychological and lifestyle patterns that shape both. This isn’t a criticism of conventional medicine. It works effectively within its diagnostic framework to rule out serious acute conditions. However, there’s a gap between 'no diagnosis' and 'everything is fine,' and many people find themselves living in that gap for years. The research published this week describes, with more precision than before, what can be happening in that gap: toxin-producing bacterial strains, a compromised gut barrier, and chronic low-grade inflammation. While these may not show up on a standard GP blood test in the early stages, they can be explored through a Functional Medicine Assessment.
What You Can Do Now
Investigate gut symptoms, don’t just manage.
If you have persistent gut symptoms such as constipation, bloating or gas, and diarrhoea that have been attributed to stress or IBS without further investigation, consider a Functional Medicine Assessment.
Gastrointestinal Mapping is a stool test that includes microbiome profiling and identifies the presence of Bacteroides fragilis among other bacterial populations (though it should be noted that current commercial tests do not identify the specific toxin-producing ETBF strain). It also covers markers of intestinal permeability alongside other factors impacting gut health, providing a more in-depth picture. This isn’t commonly available through standard NHS referral, but it is accessible through private Integrative or Functional Medicine assessment.
Prioritise oral health.
Given the strong links between oral bacteria like Fusobacterium nucleatum and colorectal cancer8, maintaining excellent oral hygiene is a critical component of gut health. Regular dental check-ups, prompt treatment of periodontal disease, and daily flossing and brushing are essential preventive measures.
You can also consider the Oralis 1 Test, developed by oral microbiome advocate Dr Victoria Sampson. It’s an at-home saliva test that assesses the oral microbiome, including the prevalence of F. nucleatum, offering a practical entry point for anyone who wants to understand what is happening in their mouth, and what that might mean for their wider health.
Support microbial diversity through diet.
A wide variety of plant foods (vegetables, fruits, wholegrains, legumes) feed different beneficial bacterial strains. The more diverse your diet, the more diverse your microbiome. Aim for variety, not just quantity.
Reduce ultra-processed food intake.
Diets dominated by industrially processed foods fuel pro-inflammatory bacterial growth. The occasional convenience meal isn’t the problem, but a diet built around them is.
Consider introducing probiotics or fermented foods.
Probiotic supplements and fermented foods such as kefir, live yoghurt, sauerkraut, and kimchi can help restore and maintain beneficial bacterial populations. Not all probiotics are equal, and strain, dose, and quality matter. If you are considering supplementation, a practitioner who understands the microbiome can guide you toward what is appropriate for you personally.
Treat stress as a Gut Health Issue, not just a mental health one.
The gut and brain communicate directly via the vagus nerve. Chronic stress elevates cortisol, which can impact gut motility and alter the composition of the microbiome, contributing to symptoms often associated with IBS.14 Stress management is essential for gut health. Whether that is breathwork, sleep prioritisation, reducing chronic overcommitment, or formal therapeutic support, addressing your stress load is a clinical intervention, not a lifestyle luxury.
Think about your antibiotic history.
If you have taken multiple courses of antibiotics in recent years, it’s worth speaking with a clinician or Functional Medicine Practitioner who understands the gut as a system. They can consider microbiome recovery and gut health support.
Use your NHS bowel cancer screening.
The UK screening programme starts at age 50 (or 45 in some regions). Take advantage of it. Early detection makes a real difference.
Do not dismiss persistent symptoms.
Blood in the stool, persistent changes in bowel habits lasting more than three weeks, unexplained abdominal pain, and unexplained weight loss all warrant a GP investigation. These aren’t symptoms to minimise or work around.
Our Position
Research like this matters because it confirms what Integrative Medicine has long recognised: the gut is more than a digestive system, the microbiome is clinically relevant, and the state of the intestinal barrier affects much more than digestion.
The mainstream medical response to this study will, rightly, focus on drug development, on ways to pharmacologically block the claudin-4 receptor. That work is important, and we welcome it.
However, our work as Integrative and Functional Medicine Practitioners is different. We investigate the gut environment that comes before the damage. We assess the microbiome, the barrier, dietary and lifestyle patterns, the inflammatory picture, and more. Then build a personalised health plan around what we find. This isn’t just symptom management. It’s a deep investigation. Ideally, it happens early, allowing us to implement preventative strategies that support optimal health before the development of chronic disease.
If this research has made you think differently about your gut health, or if you have had symptoms that have not been fully explained by conventional investigation, we would be glad to explore that with you. A Functional Medicine Assessment can evaluate gut health, nutrition, lifestyle, genetics and more to give you a clear picture of your health and how to optimise it.
Inflammation rarely announces itself with a single diagnosis. It builds up over time, and for many people, the gut is where that accumulation begins.
Book a Discovery Call with an expert practitioner to understand how Functional Medicine can support your gut health
Frequently Asked Questions
Is Bacteroides fragilis dangerous?
Most strains of Bacteroides fragilis are a normal part of the gut microbiome and cause no problems. A specific toxin-producing strain, enterotoxigenic B. fragilis (ETBF), has been linked to gut inflammation and, in research contexts, to colon cancer development. The majority of people carrying this bacterium will never develop a related condition. It is one factor within a complex picture.
What is the gut barrier, and why does it matter?
The gut barrier is the lining of the intestine, a single layer of cells held together by tight junction proteins, including claudin-4. When the barrier is intact, it controls what passes from the gut into the bloodstream. When it is compromised, pro-inflammatory substances, bacterial toxins, and undigested particles can cross it, contributing to systemic inflammation. Assessing and supporting gut barrier integrity is a central part of functional medicine gut health investigation.
Do gut bacteria cause bowel cancer?
Gut bacteria are one of several factors implicated in bowel cancer. The Johns Hopkins research identifies a specific mechanism by which one bacterial toxin initiates damage to the colon lining. This does not mean gut bacteria are the sole cause. Factors like genetics, diet, lifestyle, and environment all contribute. It confirms that the gut microbial environment is a meaningful variable in long-term bowel health.
Can I get my gut microbiome tested?
Yes. In-depth functional stool testing, including microbiome profiling, intestinal permeability markers, and inflammatory indicators, is available through private Integrative and Functional medicine clinics, including The Forbes Clinic. Our Gastrointestinal Mapping test identifies Bacteroides fragilis among other bacterial populations, though it does not identify the specific toxin-producing strain. Functional stool testing gives a more detailed picture of factors influencing gut health than standard NHS stool testing, which is primarily designed to detect infection or
blood.
Can the oral microbiome affect my risk of bowel cancer?
Research suggests it can. Fusobacterium nucleatum, a bacterium associated with gum disease, has been detected in approximately 50% of colorectal tumours studied5, and meta-analyses link periodontal disease to a significantly elevated risk of colorectal cancer.8,9 Oral health and gut health are not separate systems.
Can I get my oral microbiome tested?
Yes. Oralis 1 is an at-home saliva test developed by biological dentist Dr Victoria Sampson that profiles your oral microbiome, identifies harmful bacteria, and provides personalised recommendations.
What symptoms should I not ignore?
Blood in the stool, persistent changes in bowel habits lasting more than three weeks, unexplained abdominal pain, unexplained weight loss, and a persistent feeling of incomplete bowel emptying all warrant GP investigation. Do not manage around these symptoms. Investigate them promptly.
Research source: Sears et al., Nature (2026). Published 8 May 2026. Johns Hopkins University School of Medicine. As reported by Zoe Hardy, Daily Mail, 8 May 2026.
- Valguarnera, E. & Bubeck Wardenburg, J. (2020). Good Gone Bad: One Toxin Away From Disease for Bacteroides fragilis. Journal of Molecular Biology, 432(4), 765–785. https://doi.org/10.1016/j.jmb.2019.12.010
- Prindiville, T.P., Sheikh, R.A., Cohen, S.H., Tang, Y.J., Cantrell, M.C. & Silva, J. (2000). Bacteroides fragilis enterotoxin gene sequences in patients with inflammatory bowel disease. Emerging Infectious Diseases, 6(2), 171–174. https://doi.org/10.3201/eid0602.000210
- Shunmugavelu K, Chakravarthy BGS, Priya S. Determination of Fusobacterium nucleatum levels in patients with periodontal disease and oral squamous cell carcinoma. GMS Hygiene and Infection Control. 2025. DOI: 10.3205/dgkh000589. Available via PubMed/PMC.
- Peng X et al. Oral Fusobacterium nucleatum exacerbates ulcerative colitis via the oral-gut axis: mechanisms and therapeutic implications. Frontiers in Cellular and Infection Microbiology. 2025;15:1564169. DOI: 10.3389/fcimb.2025.1564169
- Zepeda-Rivera M et al. A distinct Fusobacterium nucleatum clade dominates the colorectal cancer niche. Nature. 2024;627:811–818. DOI: 10.1038/s41586-024-07182-w. PMC11006615.
- Han YW et al. Fusobacterium nucleatum Promotes Colorectal Carcinogenesis by Modulating E-Cadherin/β-Catenin Signaling via its FadA Adhesin. Cell Host & Microbe. 2013;14(2):195–206. DOI: 10.1016/j.chom.2013.07.012. PMC3770529.
- Gur C et al. Binding of the Fap2 Protein of Fusobacterium nucleatum to Human Inhibitory Receptor TIGIT Protects Tumors from Immune Cell Attack. Immunity. 2015;42(2):344–355. DOI: 10.1016/j.immuni.2015.01.016. PMC4361732.
- Xuan K et al. Is periodontal disease associated with increased risk of colorectal cancer? A meta-analysis. International Journal of Dental Hygiene. 2021;19(2):165–175. DOI: 10.1111/idh.12483. PMID: 33269543.
- Romero-Gámez M et al. Periodontitis and Oral Pathogens in Colorectal Cancer: A Systematic Review, Meta-Analysis, and Trial Sequential Analysis. Dentistry Journal. 2025;13(12):595. DOI: 10.3390/dj13120595. PMC12731773.
- Malesza, I.J. et al. (2024). Intestinal permeability disturbances: causes, diseases and therapy. Clinical and Experimental Medicine, 24, 234. https://doi.org/10.1007/s10238-024-01496-9
- Cancer Research UK. (2024). Bowel cancer statistics. https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/bowel-cancer
- Holohan, B., Gimeno Ruiz de Porras, D., & Bhaskaran, K. (2019). Colorectal cancer incidence among young adults in England: Trends by anatomical sub-site and deprivation. PLOS ONE, 14(12), e0225547. https://doi.org/10.1371/journal.pone.0225547
- Rasmussen, S.H. et al. (2021). Association between antibiotics and gut microbiome dysbiosis in children: systematic review and meta-analysis. Gut Microbes, 13(1). https://doi.org/10.1080/19490976.2020.1870402
- Liu, L. & Zhu, G. (2025). Gut microbiota in irritable bowel syndrome: a narrative review of mechanisms and microbiome-based therapies. Frontiers in Immunology, 16, 1695321. https://doi.org/10.3389/fimmu.2025.1695321
This article is for informational purposes only and does not constitute medical advice. If you have concerns about your gut health or bowel cancer risk, please speak with a qualified medical professional.
