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.
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.
Association of dietary patterns with risk of colorectal cancer subtypes classified by Fusobacterium nucleatum in tumor tissue, Shuji Ogino et al., JAMA Oncology, doi:10.1001/jamaoncol.2016.6374, published online 26 January 2016, abstract.
Dana-Farber Cancer Institute news release, accessed 25 January 2017 via EurekAlert.
American Cancer Society, Key statistics for colorectal cancer, accessed 25 January 2017.
Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies, Dagfinn Aune et al., The BMJ, doi: https://doi.org/10.1136/bmj.d6617, published 10 November 2011.
Red meat and colorectal cancer, Nuri Faruk Aykan, Oncology Reviews, doi:10.4081/oncol.2015.288, published online 28 December 2015.