Dysbiosis and Cancer Risk: Why a Healthy Microbiome is Crucial

In us and on us reside trillions of bacteria, fungi, and viruses that make up what is known as the human microbiome. Different regions of the body, such as the gut, skin and mouth, have their own microbiomes, harboring distinct collections of microorganisms. The most significant and well-studied of these is the gut microbiome.

A well-balanced gut microbiome aids nutrient and drug metabolism, protects the body by preventing the growth of pathogenic microorganisms, and works in a symbiotic partnership with the digestive tract and other systems in the body. Conversely, an imbalanced gut microbiome can be detrimental to our health.

An imbalance in the microbiome is known as dysbiosis. Dysbiosis can manifest with the overgrowth of a microorganism, the presence of harmful microorganisms, the absence or under-representation of beneficial microorganisms, or a lack of microbial diversity. In recent years, research has found that gut dysbiosis can contribute to the development and progression of several diseases, including cancer.

Gut dysbiosis can contribute to cancer development through:

DNA damage

DNA is the genetic information in our cells that regulates processes such as cell division. DNA damage is a critical contributor to the development of cancer, as it can inhibit cellular repair and promote uncontrolled cell division.

Harmful microorganisms in the gut microbiome can produce DNA-damaging metabolites known as genotoxins. For instance, the bacterium Campylobacter jejuni produces the genotoxin CDT, which promotes tumor formation in the intestine.

Chronic inflammation

When our bodies sustain damage, our immune systems promote inflammation to heal the injured tissue. This is the reason why an injured body part is often red, swollen, and tender to the touch. Under normal circumstances, such inflammation subsides as the tissue heals.

Chronic inflammation, however, refers to inflammation that does not heal tissue or subside in due time. It can contribute to the development of cancer through DNA damage or a compromised or overactive immune response.

Harmful microorganisms in the gut can promote chronic inflammation through the activation of specific cellular processes. For instance, a 2023 study associated the bacteria Ruminococcus gnavus, which has been implicated in inflammation, with the development of abnormal precancerous growths in the colon.

Impairing the immune system

Under normal circumstances, our immune systems also protect us from cancer by recognizing and destroying cancerous cells. Harmful microorganisms in the gut can promote cancer development by inhibiting the immune system’s ability to identify cancerous cells. One such microorganism is the bacterium Helicobacter pylori, which is widely recognized as a major risk factor for the development of stomach cancer.

The impact of the gut microbiome on cancer development and progression can also extend beyond the gut. Chronic inflammation and immune modulation as a result of harmful bacteria in the microbiome can spread to both nearby and distant organs. Research has also found that when cancers metastasize, components of the local microbiome accompany the tumor cells where they spread, aiding the development of cancer at the site of metastasis.

Dysbiosis of the microbiome in regions other than the gut can contribute to cancer development and progression as well. For example, the oral bacterium Fusobacterium nucleatum animalis clade 2 has been suggested as a primary driver of colorectal cancer in a 2024 Nature report.

The report demonstrated that within a species, closely related subspecies may have very different abilities to promote colorectal cancer. This finding emphasizes the need for extremely high-resolution microbiome tests, such as the technology behind GutID, to gain a better understanding of how cancer starts and progresses.

Escherichia coli is another species of bacterium known to reside in our intestines. While most E. coli are harmless or even beneficial, certain subtypes produce the bacterial genotoxin colibactin, which is a significant causal risk factor for colorectal cancer, particularly in young adults. Exposure to this toxin in early life can leave a unique, long-lasting mutational "fingerprint" on DNA, potentially accelerating cancer development by decades.

Proteobacteria like E. coli should be rare in healthy individuals’ gut, and amounts can be influenced by diet and drugs, unlike a genetic predisposition to cancer. Linking uncommon bacteria or pathogens to cancer risk offers a hope of controlling this risk by shaping the bacterial colonization of the gut to prevent or remove drivers of cancer.

These factors lead to the question: how can one improve the health of their gut microbiome to prevent the development of cancer?

Though each individual’s microbiome is different, certain dietary and lifestyle choices have been shown to generally contribute to a more balanced gut microbiome. These include:

Prebiotics

Prebiotics refer to ingredients in food that cannot be digested by the human body but can serve as nutrition for microorganisms in the gut. They are most abundant in plant-based, high-fiber foods, such as fruits and vegetables.

A high fiber intake is also associated with an increase in the diversity of the gut microbiome, as well as a decrease in the risk for gastrointestinal diseases. It is known to protect against cancer by reducing inflammation. Prebiotics can promote the growth of healthy commensal bacteria while inhibiting pathogens, including Proteobacteria like E. coli.

Probiotics

Probiotics refer to live microorganisms, often bacteria or yeast, that help the human body with digestion and other processes. They are most abundant in fermented foods, such as yogurt, miso, and sauerkraut, but can also be consumed in the form of supplements. Similar to prebiotic foods, probiotic foods are associated with an increase in the diversity of the gut microbiome and a decrease in the risk of gastrointestinal diseases.

Stress management

Our gut microbiome influences our mood and how we handle stress through a connection referred to as the gut-brain axis. However, since this connection is bidirectional, stress can also impact the gut microbiome in return. Excess stress impedes the delivery of nutrients to the microbiome, affecting its growth and diversity.

Stress can also weaken the mucosal barrier that protects our gut microbiome. Certain studies have found that stress management techniques like mindfulness can improve the composition of the gut microbiome.

Physical activity

Studies such as this one demonstrate that moderate to strenuous physical activity, like running, cycling, and strength training, is associated with an increase in the diversity of the gut microbiome.

In particular, exercise can enhance the growth of butyrate-producing bacteria, such as Faecalibacterium prausnitzii, in the gut. Butyrate, which is produced through the bacterial digestion of fiber, fuels the cells of our gut and regulates inflammation.

Diet, stress management, and exercise are common ways to improve the general health of the gut microbiome. However, it is important to note that each one of us has a distinct microbiome influenced by our geography, past medical history, and other lifestyle factors. For more personalized insight into your own microbiome, you may consider a gut microbiome test kit.

Gut microbiome test kits typically require you to provide a stool sample, which is then sent to a laboratory for analysis. The results from such an analysis reveal the composition and diversity of your gut microbiome.

Certain gut microbiome test kits can provide tailored insights and recommendations based on individual results. For instance, the BiomeFx test kit identifies overproduced or underproduced metabolites in the microbiome, while GutID produces a complete picture of the composition of the bacterial microbiome and uses AI-driven technology to provide prebiotic and probiotic dietary and supplemental guidance.

Such insights can be helpful for understanding individual gut health, though it is important to note that most gut microbiome test kits have not yet been clinically validated for diagnosing or screening specific health conditions and should not replace a consultation with your healthcare provider.

This article was created as an educational collaboration with GutID and is not sponsored.