A recent study suggests that intestinal microbiota may be at the heart of the association between a Western diet and colon cancer.
A healthy diet has been proved to have a huge role in the survival and prevention of cancer, particularly colon cancer, which is often caused by poor diet. According to the study, one dietary pattern may lead to colon cancer by altering bacteria in the gut.
The findings reinforce previous research linking a Western-style diet – rich in processed meat, sugar, refined grains and carbohydrates – to the disease.
The corresponding author of the study, Shuji Ogino, said: “These findings support our hypothesis that Western-style diets increase colorectal cancer risk through its effects on pks E.coli.
“This is the first study to link the western diet with specific pathogenic bacteria in cancer. Our next question is which component of Western-style diet and lifestyle relates to colorectal cancer containing this bacterial species."
The researchers, from Brigham and Women’s Hospital, Boston, USA, drew the conclusion from an analysis of data from more than 134,000 participants.
Dietary patterns were analysed alongside DNA from E.coli strains found in more than 1,000 colorectal tumours.
The focus of the study was on identifying bacterial strains carrying the distinct enzyme known as polyketide synthase (pks).
This enzyme has previously been shown to cause mutations in human cells, a key characteristic of cancer.
The team found that the Western diet was associated with colorectal tumours containing high amounts of pks+E.coli, but not tumours containing little to no amount of pks+E.coli.
The American Cancer Society explains: “Diets that include lots of vegetables, fruits and whole grains have been linked with a decreased risk of colon or rectal cancer.
“So have eating less red meat (beef, pork, or lamb) and processed meats (hot dogs and some luncheon meats), which have been linked with an increased risk of colorectal cancer."
Scientists have offered various explanations for the relationship between processed meat and cancer.
One blames heterocyclic amines (HCAs) – a byproduct of meat released during exposure to high heat.
Harvard Health adds: “HCAs may play a role, but since high levels can also be present in cooked chicken, they are unlikely to be the whole explanation.”
Another potential culprit implicated in the case of processed meats is preservatives, particularly nitrates.
These preservatives, which are converted to carcinogenic nitrosamines during digestion, aren’t present in fresh meat, however.
A more prudent dietary approach may involve higher consumption of vegetables, fruits, fish, legumes and whole grains.
Colorectal cancer, also known as colon cancer, is often referred to as hidden cancer because it rarely produces symptoms in the initial stages. The disease often affects men over 50. It arises when damaged cells acquire the ability to proliferate quickly, a process which has several known triggers.
The most effective way to diagnose the disease is with a colonoscopy, involving the insertion of a thin flexible tube with a camera on the end through the anus and up through the colon. The camera will help doctors identify any polyps, which will be removed during the procedure and sent to a laboratory for testing.
Study details
Western-style Diet, pks Island-Carrying Escherichia coli, and Colorectal Cancer: Analyses from Two Large Prospective Cohort Studies
Kota Arima, Rong Zhong, Tomotaka Ugai, Melissa Zhao, Koichiro Haruki, Naohiko Akimoto, Mai Chan Lau, Kazuo Okadome, Raaj S. Mehta, Juha P. Väyrynen, Junko Kishikawa, Tyler S. Twombly, Shanshan Shi, Kenji Fujiyoshi, Keisuke Kosumi, Yoko Ogata, Hideo Baba, Fenglei Wang, Kana Wu, Mingyang Song, Xuehong Zhang, Charles S. Fuchs, Cynthia L. Sears, Walter C. Willett, Edward L. Giovannucci, Jeffrey A. Meyerhardt, Wendy S. Garrett, Curtis Huttenhower, Andrew T. Chan, Jonathan A. Nowak, Marios Giannakis, Shuji Ogino.
Published in Gastroenterology on 24 June 2022
Abstract
Background and aims
Evidence supports a carcinogenic role of Escherichia coli carrying the polyketide synthase (pks) island that encodes enzymes for colibactin biosynthesis. We hypothesised that the association of western-style diet (rich in red and processed meat) with colorectal cancer incidence might be stronger for tumours containing higher amounts of pks+ E. coli.
Methods
Western diet score was calculated using food frequency questionnaire data obtained every four years during follow-up of 134,775 participants in two U.S.-wide prospective cohort studies. Using quantitative polymerase chain reaction, we measured pks+ E. coli DNA in 1,175 tumours among 3,200 incident colorectal cancer cases that had occurred during the follow-up. We utilised the 3,200 cases and inverse probability weighting (to adjust for selection bias due to tissue availability), integrated in multivariable-adjusted duplication-method Cox proportional hazards regression analyses.
Results
The association of the western diet score with colorectal cancer incidence was stronger for tumours containing higher levels of pks+ E. coli (Pheterogeneity = 0.014). Multivariable-adjusted hazard ratios (with 95% confidence interval) for the highest (vs. lowest) tertile of the western diet score were 3.45 (1.53-7.78) (Ptrend = 0.001) for pks+ E. coli-high tumours, 1.22 (0.57-2.63) for pks+ E. coli-low tumours, and 1.10 (0.85-1.42) for pks+ E. coli-negative tumours. The pks+ E. coli level was associated with lower disease stage but not with tumour location, microsatellite instability, or BRAF, KRAS, or PIK3CA mutations.
Conclusions
Western-style diet is associated with higher incidence of colorectal cancer containing abundant pks+ E. coli, supporting a potential link between diet, the intestinal microbiota, and colorectal carcinogenesis.
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