Gut Bacteria and Your Colon Cancer Risk Factors

By Katharine Paljug @kpaljug
May 09, 2017

What you eat affects your colon cancer risk factors, but you can change your gut bacteria from bad to good and reduce your risk of cancer with these simple foods.

Colorectal cancer, or cancer that first develops in the colon or rectum, is the fourth most common cancer in the United States. For both men and women, the National Cancer Institute reports, it is also the second most deadly.

There are many causes of cancer, no matter where it first develops. But a study, by researchers from the Dana-Farber Cancer Institute of the Harvard T.H. Chan School of Public Health, reports that your risk of developing colon cancer could be affected by something literally microscopic: the bacteria in your intestines.


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Diet and colon cancer risk

The link between the gastrointestinal system and colon cancer isn’t entirely surprising. Previous research has shown a relationship between diet and cancer.

One 2015 study found that diets high in red meat increased risk for colorectal cancer, while other research has shown a relationship between eating high levels of processed meat and an increased likelihood of colon cancer.

Sugar has also come under scrutiny. One study found that diets high in sugar and simple carbohydrates increase colon cancer risk factors, possibly by impacting glucose levels in the blood.

But the Harvard study takes diet a step further, examining the interaction between your diet, your gut bacteria, and your risk for cancer.

Gut bacteria and colon cancer

The Harvard team focused on F. nucleatum, or Fusobacteria, a particular type of bacteria that is associated with high levels of disease and infections in the body. F. nucleatum has been investigated for its role in health conditions, including gum disease, preeclampsia, Alzheimer’s disease, and appendicitis.

In recent years, as researchers began to examine the role that gut bacteria plays in gastrointestinal diseases, multiple studies have found that F. nucleatum is often present in tumors that develop in the colon and rectum.

Further research seemed to indicate that this wasn’t just a correlation; animal studies and a review of the evidence in human studies indicated that the Fusobacteria play a role in causing cancer in the colon and rectum.

The effect of a high fiber foods on colorectal cancer

Building on previous research which showed that people who ate high fiber foods had healthier gut bacteria, as well as higher levels of F. nucleatum in their stool but not their intestines, the Harvard study looked at the effect of a high fiber diet on the development of colorectal tumors.

Researchers analyzed data from over 137,000 adults who participated in the Nurses’ Health Study or the Health Professionals Follow Up Study. Over an average of 26 to 32 years, there were 1,019 cases of colorectal cancer in the study group. The researchers analyzed tissue samples from these tumors and used data from questionnaires to learn about the participants’ diet and fiber intake.

They found that those who followed a high fiber diet, also known as a “prudent diet,” were less likely to have tumors containing the F. nucleatum bacteria.

The data, said co-senior author Shuji Ogino, MD, PhD, provide “compelling evidence” that gut bacteria can influence your risk of developing cancer. “Though our research dealt with only one type of bacteria, it points to a much broader phenomenon – that intestinal bacteria can act in concert with diet to reduce or increase the risk of certain types of colorectal cancer,” Ogino concluded.

How to improve gut bacteria: Eat high fiber foods

Though researchers don’t yet know exactly what causes the link between bacteria, fiber, and cancer in the colon, many theorize that too little dietary fiber could lead to inflammation, causing an increased growth in unhealthy bacteria.

Increasing the amount of fiber in your diet, then, could decrease inflammation in your gastrointestinal system, promoting a healthy gut biome and protecting you against colon and rectal cancers.

Adding more plant-based food to your diet will increase your fiber intake. Fruit and vegetable choices with high levels of fiber include artichokes, berries, green leafy vegetables, avocados, and pears. Oatmeal and whole wheat bread are high fiber options for breakfast. And if you want to avoid red and processed meat, legumes and pulses — such as beans, lentils, and split peas — are rich in both fiber and protein.


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March 18, 2020

Reviewed By:  

Christopher Nystuen, MD, MBA