How Does a Western Diet Cause Colon and Rectal Cancer? A New Perspective

New research examined the link between a Western diet and tumors with abundant polyketide synthase (pks+) Escherichia coli bacteria, finding a strong association with a subgroup of colorectal (large bowel) cancer. This supports the connection between diet, gut microbiota and colorectal carcinogenesis (cancer formation).

Researcher Shuji Ogino, from the Department of Pathology at Brigham and Women's Hospital in Boston, said that colibactin-producing pks+ E.coli had recently been found to cause DNA mutations in cells of the large intestine. “Our findings have successfully linked Western dietary patterns to this bacterium in colorectal cancer.”

The study was published online in Gastroenterology, the journal.

The Link Between Diet, Gut Bacteria and Cancer Formation

Western dietary patterns, rich in red and processed meat, sugar and refined grains but low in vegetables and legumes, have been shown to cause systemic and intestinal inflammation in the body.

The study team explained, "Given the possible interaction between diet and harmful gut bacteria, examining a Western diet in relation to pks+ E.coli in colorectal tumor tissue is particularly interesting," they said.

For this study, Western diet scores were calculated using food-frequency data obtained every 4 years from 134,775 adults in the Health Professionals Follow-up Study and the Nurses' Health Study. Among 1175 colorectal cancer tumors, pks+ was detected in 111 tumors as E.coli , while the remaining 1064 tumors tested negative for these bacteria.

The results showed that the association of Western diet scores with colorectal cancer incidence (frequency of occurrence) differed according to pks+ E.coli levels, and that tumors with higher levels of pks E.coli were strongly associated with a Western diet.

In individuals with the highest (and lowest) Western diet scores, multivariable hazard ratios for tumors containing high levels of pks+ E.coli were 3.45; for those containing low levels of pks+ E.coli they were 1.22; and for colorectal cancer tumors with no detectable pks+ E.coli the ratio was 1.10.

The researchers explained, "Our findings provide evidence supporting the role of gut microbiota in mediating the pathogenic link between diet and colorectal cancer," they said.

Although more studies are needed, Ogino said the findings have potential clinical implications. "People with Western dietary patterns have a higher risk of colorectal cancer. These high-risk individuals probably need more examination than low-risk people because of their dietary patterns. They most likely need personalized cancer screening." Ogino said the study also highlighted the importance of dietary changes for cancer prevention.

Evidence-Based Dietary Recommendations

Dr. Aasma Shaukat of the Division of Gastroenterology and Hepatology at NYU Langone Health in New York commented on the study, "It contributes to our understanding of how diet may affect colorectal cancer risk,” she said. "Although this does not affect recommendations for cancer screening, it shows that we should continue to recommend a diet low in red meat and refined sugar, together with other lifestyle changes, for colorectal cancer prevention."

Also offering an outside perspective, Amanda Bode of the Cleveland Clinic Center for Human Nutrition noted that the Western dietary factors proposed in this study to increase inflammation, lead to DNA damage and cause colorectal cancer were "not surprising." "There is substantial evidence from many other studies that dietary patterns including red meat, refined grains and sugar increase colorectal cancer risk. As an oncology dietitian, this research reinforces the advice I would generally give a patient for colorectal cancer prevention or survival. In addition to recommending limiting processed meat and eating fewer refined grains and less sugar, a registered dietitian can help identify issues related to the gut microbiome and individualize dietary interventions while considering each patient’s personal preferences."

For example, a registered dietitian may help a patient identify commonly consumed foods known to be associated with a high risk of colorectal cancer and replace them with foods that improve beneficial gut bacteria.

"Working to improve the overall dietary pattern seems to affect disease risk more than focusing on a single food."

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