Hailing from the Dana-Farber Cancer Institute of the Harvard T.H. Chan School of Public Health in Boston, the study's lead researcher Dr. Shuji Ogino and his colleagues published their findings in JAMA Oncology.
Past research has shown that diets laden with red meat and processed meats can increase the risk of cancer, while diets that are rich in fruits, vegetables and whole grains tend to decrease cancer incidence. Previous studies have also indicated that one way in which diet may contribute to cancer risk is through alterations to the bacterial populations that inhabit the gut, also known as the microbiome.
The new study by Dr. Ogino and his team serves to support these past findings, and their data show that people who follow a high-fiber diet are less likely to develop colorectal tumors that contain the bacterium F. nucleatum. This is important because Fusobacterium nucleatum is thought to play a role in the development of colorectal cancers, by suppressing the body's immune response to the tumor. The research team also notes that evidence has suggested that diet can influence the presence of F. nucleatum in the gut.
"One study showed that F. nucleatum in the stool increased markedly after participants switched from a prudent to a Western-style, low-fiber diet," Dr. Ogino explains. "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."
The researchers defined a "prudent diet" as one that was rich whole grains and fiber, while a "Western diet" was defined as one that is primarily comprised of red and processed meats, refined grains and sweets -- exactly as you'd expect. Dietary data was gathered at 2 to 4-year intervals between the years of 1980 and 2010, which were then used to calculate nutrient and fiber intake.
To put their hypothesis to the test, the researchers utilized and examined data from 137,217 individuals who were a part of either the Nurses' Health Study or the Health Professionals Follow-Up Study.
Follow-up years had an average range of 26 to 32 years. During that time, there were 1,019 cases of colorectal cancer identified among the participants. And between March 2015 and August 2016, Dr. Ogino and his team analyzed tissue samples from all the study subjects who had colorectal cancer, specifically focusing on the F. nucleatum content of the samples.
The team found that participants who followed a prudent diet were substantially less likely to develop colorectal cancers containing the bacterial species when compared to those following a Western diet. Participants following a high fiber diet were, however, not less likely to develop a colon cancer that was free of the F. nucleatum bacteria.
In their conclusion, the researchers write, "Prudent diets rich in whole grains and dietary fiber are associated with a lower risk for F nucleatum–positive colorectal cancer but not F nucleatum–negative cancer, supporting a potential role for intestinal microbiota in mediating the association between diet and colorectal neoplasms."
Overall, it seems that the importance of a robust microbiome cannot be underestimated in relationship to disease -- especially when it comes to how the two may work together.