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  • A new nationwide study adds to mounting evidence that a standard Western diet pattern may contribute to colorectal cancer (CRC) onset.
  • The research suggests that these nutrient-poor foods encourage the development of CRC tumors through their effect on the gut microbiota.
  • Scientists found a strong link between Western-style dietary patterns and CRC tumors containing elevated amounts of pks+ Escherichiacoli bacteria.
  • Researchers have also discovered another bacterial byproduct that may suppress CRC tumor growth.

Colorectal cancer (CRC) is any cancer affecting the colon, hence “colo,” and rectum, hence “rectal”. It is the third most common and second deadliest diagnosed cancer in the United States, claiming over 50,000 lives every year.

Researchers from Brigham and Women’s Hospital in Boston, MA recently observed that CRC tumors with high levels of pks+ E. coli bacteria correlate with diets rich in red and processed meats and empty calories.

They believe that unhealthy foods may stimulate the cancer-inducing activity of colibactin, a substance deriving from E. coli, in the gut.

Their findings appear in Gastroenterology.

Dr. Shuji Ogino, chief of the Molecular Pathological Epidemiology Program in the Department of Pathology at Brigham and Women’s Hospital, was the study’s corresponding author.

E. coli is a normal part of the gut microbiome. However, certain strains of this bacterium hold a distinct cluster of genes known as the polyketide synthase (pks) island.

These pks+ E. coli strains produce colibactin, a toxic metabolite that can damage DNA and trigger cellular mutations that promote CRC.

Consumption of a typical Western diet — also sometimes called an “American diet” — consisting mainly of red and processed meats, sugar, and refined carbohydrates, can cause intestinal and systemic inflammation, precursors to colorectal tumors.

A poor diet is also tied to an imbalance of intestinal microbiota, another factor related to CRC. Furthermore, prior studies have linked E. coli and other bacteria to this cancer.

Consequently, Dr. Ogino and his team suspected that a Western diet might induce a stronger risk for tumors with considerable amounts of pks+ E. coli. Up to this point, though, they did not know whether the diet’s correlation with CRC varies by gut bacteria.

The researchers combed through two nationwide studies to see how Western diets may influence intestinal microbe activity and the odds of CRC occurrences.

The Nurses’ Health Study included 121,700 women aged 30 to 55 at enrollment in 1976. The Health Professionals Follow-up Study included 51,529 males ages 40 to 75 years at enrollment in 1986.

These studies provided detailed insight into 30 years of medical and dietary history of its subjects. They presented “a unique opportunity to examine long-term dietary patterns of individuals — who had not known whether they would develop cancers or not — in relation to CRC incidence subclassified by pks+ E. coli levels.”

The data were adjusted for potential selection bias and factors such as body mass index (BMI), physical activity, tobacco and alcohol consumption, and family history of CRC.

A total of 134,775 of the two studies’ participants provided enough dietary information to be included in this analysis. Among these, the researchers found 3,200 CRC cases.

The team also extracted DNA from archived tissue sections of colorectal tumors to find pks+ E. coli strains.

The researchers admitted that their study comes with several limitations.

More studies are needed to confirm how the overall Western diet or specific foods and pks+ E. coli may work together to promote CRC.

Speaking with Medical News Today, Dr. Ogino acknowledged that the research population was mostly non-Hispanic Caucasian. However, he cited evidence of a growing trend of early-onset CRC among other ethnicities.

Dr. Ogino and fellow scientists found sex-specific differences in pks+ E. coli colorectal cancer occurrences, but the underlying mechanisms are still unclear.

Measurement errors and unintentional mixing of the effects of factors may have skewed some results as well.

While colibactin in CRC tumors encourages cancer growth, some researchers believe that a healthy gut microbiome may halt tumor progression.

University of Michigan scientists recently found that the metabolite reuterin, produced by the bacteria Lactobacillus reuteri, shows potent anticancer potential in CRC cell lines and in vivo.

At the National Comprehensive Cancer Network 2022 Annual Meeting, lead investigator Joshua Goyert, of the University of Michigan Medical School Rogel Cancer Center, said that the gut microbiome, and especially reuterin, can “reduce oxidative stress in CRC cells and inhibit tumor proliferation and tumor volume in in vivo models.”

Dr. Ogino said that this study is among the first to associate the Western diet with specific disease-causing bacteria in cancer.

Ultimately, he believes that this research demonstrates how dietary choices may help prevent CRC.

Dr. Ogino commented emphatically:

“As a society, we do not generally recognize the importance of prevention. Rather, we always regret after harms happen (e.g., cancer occurs). We need to change our mindsets and become proactive. Media is very hot about new treatment for end-stage cancer patients, which may prolong life for a few months. While this is important, it is much better to prevent. If we can prevent 10% of colorectal cancer cases, 150,000 new CRC cases each year — in the U.S. — would become 135,000 new CRC cases. You can see 15,000 people each year do not need suffer side effects of treatment or surgery. This would be a big impact.”