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.

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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.

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.

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.

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