Gut Bacteria Mediate Link Between Diet and Colorectal Cancer

New research provides further evidence that what we eat alters gut bacteria to affect colorectal cancer risk, after linking a high-fiber diet to a reduced risk of colorectal cancer containing Fusobacterium nucleatum.
[Illustration of gut bacteria in the intestine]
Researchers have found that a high-fiber diet could reduce the risk of colorectal cancer containing the bacterium F. nucleatum.


Study leader Dr. Shuji Ogino - from the Dana-Farber Cancer Institute of the Harvard T.H. Chan School of Public Health in Boston, MA - and colleagues report their findings in JAMA Oncology.

Colorectal cancer, which is a cancer that begins in the colon or rectum, is the third most common cancer among men and women in the United States.

In 2017, it is estimated that there will be 95,520 new cases of colon cancer and 39,910 new cases of rectal cancer diagnosed in the U.S.

Studies have shown that a diet high in red and processed meats may increase the risk of colorectal cancer, while a high-fiber diet - rich in fruits, vegetables, and whole grains - has been associated with a lower risk of the disease.

Previous research has suggested that one way by which diet influences the risk of colorectal cancer is through the changes it makes to the gut microbiome (the population of microorganisms that live in the intestine).

The new study from Dr. Ogino and team supports this association, after finding that individuals who followed a high-fiber diet were at a lower risk of developing colorectal cancer tumors containing the bacterium F. nucleatum.

F. nucleatum and colorectal cancer

According to Dr. Ogino, recent research has shown that F. nucleatum may play a role in the development of colorectal cancer.

"One study showed that F. nucleatum in the stool increased markedly after participants switched from a prudent to a Western-style, low-fiber diet," he added. "We theorized that the link between a prudent diet and reduced colorectal cancer risk would be more evident for tumors enriched with F. nucleatum than for those without it."

To test their theory, the researchers analyzed the data of 137,217 individuals who were a part of either the Nurses' Health Study or the Health Professionals Follow-Up Study.

Over an average 26-32 years of follow-up, there were 1,019 cases of colorectal cancer identified among the participants.

Between March 2015 and August 2016, the team analyzed tumor tissue samples from all patients with colorectal cancer, focusing on whether the samples contained F. nucleatum.

Dietary data for each participant was gathered using food frequency questionnaires completed at 2-4-year intervals between 1980 and 2010. These data were used to calculate total nutrient intake and total fiber intake.

Gut bacteria 'act in concert with diet' to affect colorectal cancer risk

The team found that participants who followed a prudent diet - defined as a high intake of vegetables, fruits, whole grains, and legumes - were at a significantly lower risk of colorectal cancer containing F. nucleatum, compared with subjects who followed a Western-style diet.

However, participants who had a prudent dietary pattern did not show a reduced risk of colorectal cancer that was free of F. nucleatum.

Dr. Ogino says that these findings provide "compelling evidence" that diet influences the likelihood of developing specific forms of colorectal cancer by altering the gut microbiome.

"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."

Dr. Shuji Ogino


The researchers conclude that further studies are needed to confirm their findings, and larger-scale studies should delve into the complex relationship between diet, gut bacteria, and cancer.

Honor Whiteman
Published :


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How to Improve Your Gut Health


Our bodies host around 100 trillion bacterial organisms, which populate our skin, nose, urogenital tract, but the majority are found in the digestive system. These bacteria are known as the micro-biome, or gut flora. Amazingly, the bacterial cells in our gut outnumber our body cells 10 to 1!

They play essential roles in the body. The complex function and interrelationship between our gut flora and health and disease is becoming ever more apparent. There are links between gut bacteria and a staggering variety of disorders and diseases, including allergies (1), irritable bowl syndrome (2), obesity and even autistic spectrum disorders (3). They play a role in immune health, digestion, metabolism and synthesis of certain nutrients. This sensitive eco-system residing in our intestines is composed of over 400 different strains of bacteria (4) and influenced heavily by diet and stress.


Immune function: Gut bacteria are a crucial line of resistance to invading microbes. The bacteria stimulate the production of lymph tissue, promoting the production of antibodies which allow us to recognize invading pathogens (5) and subsequently fight off infection.

Complete digestion: The bacteria break down otherwise indigestible plant materials from our diet. They break down carbohydrates to create up to 10% of our daily energy intake.

Synthesis of certain nutrients: B vitamins and vitamin K are synthesized by our gut biome and play essential roles in the body. B vitamins are associated with energy production and nerve function. Vitamin K on the other hand is crucial in effective blood clotting.


What you really want to know is how do you maintain a healthy gut and even improve gut health? The first step is to eliminate food and other products that are harmful to our bacteria.

Antibiotics and or other antibacterial drugs often play a crucial, life-saving role in serious situations. However, these drugs are widely overprescribed. One course of antibiotic treatment is enough to do serious damage to your gut flora, so request to use them as a last resort from your health care practitioner.

Other antibacterial products, including popular toothpaste brands, can contain triclosan, an antibacterial and antifungal agent. triclosan has been shown to modify our gut flora (6) and should be avoided when possible.

Eliminate other inflammatory food products, which can harm gut flora including sugar, alcohol and gluten.


Prebiotics, not to be confused with probiotics, are a special form of dietary fiber, which nourish and feed the healthy bacteria already in our gut. Eating a healthy dose of prebiotic containing foods can help shift the balance in favor of beneficial bacteria.

There are two basic types fiber in our foods; these are insoluble fiber, which is not fermented by the gut’s bacteria, and soluble fiber, which is fermented by the gut flora.

Soluble fibers can be found in foods such as sweet potato, yam, lentils, apple and oranges, and provide excellent prebiotic qualities. Insoluble fibers can be found in dark green leafy vegetables such as broccoli and kale. Both soluble, and insoluble starches have been shown to beneficially change the composition of the gut flora in as little as two weeks (7). Try adding more fruit and vegetables to your diet as the first step to improving your gut health.


After the introduction of more fruit and vegetables to your diet, try eating fermented foods like kefir, yogurt, sauerkraut and kombucha, which all contain beneficial live bacterial strains such as Lactobacillus and Bifidobacterium to help boost friendly bacteria. These can be purchased in some shops, but you can also make your own for a fraction of the price.

Also consider taking a probiotic supplement containing strains such as Lactobacillus acidophilus and Bifidobacterium lactis. It should contain at least 50 billion bacteria per serving. And as with most supplements, you get what you pay for, so spend a little extra on a safe, reputable brand.


Collagen not only has a role in maintaining connective tissue and joints, but it plays an important role in digestion. Collagen supplementation can help repair the gut wall, reducing what is known as ‘leaky gut,’ reducing inflammation and protects our vital bacterial diversity. Try eating a homemade bone broth or collagen peptide supplement.



1. Stefka, Andrew T., et al. “Commensal bacteria protect against food allergen sensitization.” Proceedings of the National Academy of Sciences 111.36 (2014): 13145-13150.

2. Pyleris, Emmannouil, et al. “The prevalence of overgrowth by aerobic bacteria in the small intestine by small bowel culture: relationship with irritable bowel syndrome.” Digestive diseases and sciences 57.5 (2012): 1321-1329.

3. Moyer, Melinda. “Gut Bacteria May Play a Role in Autism.” Scientific American (2014)

4. Levinson, Warren, and Ernest Jawetz. Medical microbiology and immunology: examination and board review. Appleton & Lange, 1996.

5. Guarner, Francisco, and Juan-R. Malagelada. “Gut flora in health and disease.” The Lancet 361.9356 (2003): 512-519.

6. Pasch, Erica, et al. “Effects of triclosan on the normal intestinal microbiota and on susceptibility to experimental murine colitis.” The Journal of the Federation of American Societies for Experimental Biology (2009).

7. Venketeshwer Rao, A., et al. “Effect of fiber-rich foods on the composition of intestinal microflora.” Nutrition Research 14.4 (1994): 523-535.

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