Colorectal cancer has been on the rise among children, adolescents, and young adults in recent years, and this has been a source of concern for health practitioners and researchers. Scientists are now attempting to create the possible connections between diet, gut microbiota structure, and the incidence of colorectal cancer.
Scientists at the University of Toronto in Canada conducted a study recently where they analyzed the interactions between different dietary patterns and specific strains of bacteria in the gut. By combining three diets with three strains of bacteria, they wished to determine whether there were combinations that would result in an increased risk of the development of colorectal cancer. What they discovered was that a low-fiber, low-carbohydrate diet, when combined with a specific strain of Escherichia coli (E. coli), significantly increased the formation of polyps in the colon. If left untreated, these polyps would have formed into colorectal cancer.
How Gut Bacteria Influence Cancer Development
Colorectal cancer is one of the most common cancers diagnosed in the United States. Statistics indicate that one in 24 men and one in 26 women will develop colorectal cancer in their lifetime. Alarming statistics show that diagnoses of colorectal cancer in adults aged 30 to 34 years have risen by 71%, and those aged 35 to 39 years have seen a 58% rise between 1999 and 2020.
While colorectal cancer cannot be entirely prevented, scientists have discovered that the following lifestyle modifications can lower the risk:
- Avoiding tobacco
- Consuming less alcohol
- Following a diet rich in whole grains, fruits, and vegetables
- Reducing the level of processed food and red meat intake
Because there is such a powerful connection between diet and colorectal cancer, scientists are attempting to identify whether specific bacterial strains in the gut interact with diet to influence cancer risk.
In this study, researchers examined the effects of three bacterial strains:
- Bacteroides fragilis
- Helicobacter hepaticus
- Escherichia coli (E. coli)
These bacteria have already been linked to cancer risk since they are able to induce DNA damage in intestinal cells. This may be done directly, by generating genotoxins that are damaging, or indirectly, by inducing inflammation that leads to genetic mutations.
The Influence of Diet on Gut Bacteria and Cancer Risk
For their research, scientists fed mice different diets, including:
- A low-carbohydrate, low-fiber diet
- A normal diet (normal chow)
- A Western-style diet (high sugar and fat)
Over nine to sixteen weeks, scientists watched the mice for polyp formation and other signs of colorectal cancer. They discovered that only the combination of a low-carbohydrate diet and exposure to E. coli significantly affected cancer risk.
This is particularly concerning given that 60% of colorectal cancer cases are triggered by E. coli infections. The study found that mice on the low-carb diet had:
More tumors and polyps, which are precursors to colorectal cancer
More DNA damage from the presence of colibactin, a genotoxin produced by E. coli
Thinning of the protective mucus layer in the colon, which allows harmful microbes to devastate intestinal cells
Inflammation and imbalance of gut microbiome that creates a pro-cancer environment
Could Fiber Reverse These Effects?
Perhaps the most important result from the study was the benefit of dietary fiber. When the researchers supplemented the mice’s diets with fiber, they observed that tumor formation was reduced and control of inflammation was enhanced.
Dr. Marianne Cusick, associate professor of colon and rectal surgery at UTHealth Houston, spoke on the implications of the study, stating:
The researchers found that mice developed colorectal cancer due to a low-carb diet paired with a colibactin-producing strain of E. coli. The reason is that there is greater inflammation, a thinner mucus barrier, and more polyps.”
She emphasized the importance of having a healthy mucus barrier in the colon that can be supported by soluble fibers found in foods like:
- Inulin (found in onions, garlic, and bananas)
- Pectin (found in apples, citrus fruits, and carrots)
- Beta-glucan (found in oats, barley, and mushrooms)
These fibers serve as food for friendly gut bacteria, which leads to the production of short-chain fatty acids (SCFAs) like butyrate, which strengthen the mucus layer and foster overall gut health.
The Future of Research on Diet and Gut Microbiome
MemorialCare Todd Cancer Institute board-certified oncologist and hematologist Dr. Nilesh Vora noted that while this study is interesting, additional research is needed to determine if the same occurs in humans.
There may be a real relationship here that could explain the rising incidence of colorectal cancer, but more work needs to be done. The gut microbiome is a very new area of research in the field of colon cancer, and we can expect a great deal of new information in the next several years.”
The team’s future plans involve:
- Investigating which kinds of fiber are most protective
- Conducting human trials to confirm the link between diet, E. coli, and colorectal cancer
- Exploring targeted therapies or diets that can reduce the risk of cancer
