The intestinal microbiota: an intermediary between diet and colorectal cancer
A diet rich in fiber reduces the risk of colorectal cancer associated with the presence of Fusobacterium nucleatum.
Previous studies have shown that F. nucleatum seems to play an important role in colorectal cancer, considering its overrepresentation in the intestinal microbiota of patients with this particular cancer and its ability to suppress the host’s immune response against the tumor. Diet directly influences the prevalence of these bacteria in the intestinal microbiota: people who move from a high-fiber diet to a low-fiber diet see concentration of F. nucleatum increase in their stool.
Starting from this observation, an American team put forth a hypothesis that the bacteria might play an intermediary role between diet and an increased risk of colorectal cancer. The researchers carried out a prospective study using the data from the Nurses’ Health Study (NHS) and Health Professionals Follow-up Study (HPFS) cohorts, including 137,217 participants. They classified individuals based on their diet: high in whole grains and fiber (“prudent” diet) or high in red meat, refined grains, and sugar (Western diet, which increases cancer risk) and studied the 1019 cases of colorectal cancer that occurred in the 26 to 32 years of the study. They systematically searched for the presence of F. nucleatum in the tumors (biopsies) after extracting and amplifying the DNA present in the search for bacterial DNA. The results showed that those who followed a “protective” diet (high fiber diet) presented a relative risk of F. nucleatum-positive cancer (presence of F. nucleatum in the tumor) that was reduced by 57% compared to those who followed a Western diet (low fiber diet). However, no association was found for F. nucleatum-negative cancer (absence of F. nucleatum in the tumor).
The analysis of the associations between these kinds of tumors and various macronutrients, however, shows that cereal grain fibers might be responsible for the observed reduction of the F. nucleatum-positive tumor risk, and not fat or protein. These data reinforce the idea that the protective effect of these diets come from the intestinal microbiota, and in particular the presence of F. nucleatum, since the effect of the fiber only works in F. nucleatum-positive patients.
Metha RS et al. Association of Dietary Patterns With Risk of Colorectal Cancer Subtypes Classified by Fusobacterium nucleatum in Tumor Tissue. JAMA Oncol. 2017 Jul 1;3(7):921-927. doi: 10.1001/jamaoncol.2016.6374.