New Insight on How a Western Diet May Cause Colorectal Cancer

Megan Brooks

July 01, 2022

New research points to a strong association between a Western-style diet and a subgroup of colorectal cancer (CRC) containing abundant polyketide synthase (pks+) Escherichia coli, supporting a potential link between diet, the intestinal microbiota, and colorectal carcinogenesis, the researchers say.

Colibactin-producing pks+ E coli was recently found to cause DNA mutations in colonic cells, study investigator Shuji Ogino, MD, PhD, Department of Pathology, Brigham and Women's Hospital, Boston, told Medscape Medical News.

"Our findings successfully linked Western-style diets with this bacteria in colorectal cancer. Our study supports a hypothesis that Western-style diet can cause colorectal cancer via this bacteria," Ogino said.

The study was published online in Gastroenterology.

Interplay Between Diet and Pathogenic Bacteria

Western-style diets, which are high in red and processed meat, sugar, and refined grains and low in vegetables and legumes, have been shown to induce systemic and intestinal inflammation.

"Considering the possible interplay between diet and pathogenic bacteria, it is of particular interest to study Western-style diet in relation to pks+ E coli within colorectal tumor tissue," the study team writes.

They calculated Western diet scores using food frequency data obtained every 4 years in 134,775 adults participating in the Health Professionals Follow-up Study and the Nurses' Health Study.

Among 1175 CRC tumors, they detected pks+ E coli in 111 tumors, whereas the remaining 1064 tumors were negative for this bacterium.

The results showed that the association of Western diet scores with CRC incidence differed by pks+ E coli levels and was stronger for tumors containing higher levels of pks+ E coli.

Multivariable hazard ratios in individuals with the highest (vs lowest) Western diet scores were 3.45 for tumors with high-level pks+ E coli, 1.22 for those with low-level pks+ E coli, and 1.10 for CRC tumors without detectable pks+ E coli.

"Our findings provide evidence supporting the role of the gut microbiota in mediating the pathogenic link between diet and colorectal cancer," the authors write.

Although more studies are needed, Ogino said the findings have potential clinical implications.

"Persons with Western-style diets are at increased risk of colorectal cancer. These high-risk individuals, because of their diet, likely need more scrutiny than low-risk people. They most likely need personalized cancer screening," Ogino said.

The study also underscores the importance of dietary modifications for cancer prevention, Ogino said.

Support for Current Dietary Advice

Reached for comment, Aasma Shaukat, MD, MPH, with the Division of Gastroenterology and Hepatology at NYU Langone Health in New York, said this study "adds to our understanding of how diet may influence risk of colorectal cancer."

"While this does not affect recommendations on screening, it suggests we should continue to recommend a diet low in red meat and refined sugar for CRC prevention, along with other lifestyle changes," Shaukat told Medscape Medical News.

Also providing outside perspective, Amanda Bode, RDN, LD, with the Cleveland Clinic Center for Human Nutrition, noted that the dietary factors of the Western diet that have been suggested in this study to increase inflammation, leading to the DNA damage and colorectal cancer, are "not surprising."

"There is substantial evidence from many other studies that dietary patterns, including red meat, refined grains, and sugar, increase colorectal cancer risk," Bode told Medscape Medical News.

"As an oncology registered dietitian, this research study reinforces the advice I would typically give to a patient for prevention or survivorship of colorectal cancer," Bode added.

"In addition to the recommendations to limit processed meat and eat less refined grains and sugar, a registered dietitian can help identify issues with the intestinal microbiome and individualize nutrition interventions with each patient's unique preferences in mind," she noted.

For example, a registered dietitian can help a patient identify foods commonly consumed that are known to be associated with a high risk for colorectal cancer and substitute them for foods that improve beneficial bacteria in the gut, she explained.

"Working toward improving the dietary pattern overall seems to impact disease risk more than just the focus on an individual food," Bode said.

This work was supported in part b y grants from the US National Institutes of Health, Cancer Research UK, Stand Up to Cancer, Project P Fund, The Friends of the Dana-Farber Cancer Institute, Bennett Family Fund, and the Entertainment Industry Foundation through National Colorectal Cancer Research Alliance. Ogino, Shaukat, and Bode report no relevant financial relationships.

Gastroenterology. Published online June 24, 2022. Abstract

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