Low-carb diets, such as the popular keto diet, have gained significant attention for their weight loss benefits. However, recent research suggests that these diets may come with unexpected risks, particularly concerning colorectal cancer.
A study from the University of Toronto explored how low-carb diets affect bacteria linked to colorectal cancer. Researchers focused on mice and tested the effects of low-carb, standard, and Western diets on the growth of different bacterial strains. The goal was to examine how these diets might influence bacteria that contribute to colorectal cancer.
The findings, published in Nature Microbiology, revealed a concerning link between low-carb diets and a type of Escherichia coli (E. coli). The research showed that these diets could increase the development of polyps, some of which may evolve into colorectal cancer. This discovery raises questions about the long-term health impacts of low-carb diets.
How Certain Bacteria Might Contribute to Cancer
Colorectal cancer, which affects the colon and rectum, is one of the most common cancers in the United States. It impacts 1 in 24 men and 1 in 26 women. Recent data shows a sharp rise in cases among adults aged 30 to 39, with a 71% increase in those aged 30 to 34 between 1999 and 2020.
While lifestyle changes like quitting smoking, reducing alcohol consumption, and eating more fruits, vegetables, and whole grains can lower cancer risk, no method guarantees complete prevention. Researchers are now investigating whether diet, specifically the presence of certain bacteria, plays a role in the development of colorectal cancer.
In this study, the researchers focused on three specific bacteria: Bacteroides fragilis, Helicobacter hepaticus, and E. coli. These bacteria were introduced into the mice to examine how they might affect the colon. The authors noted that these microorganisms can damage DNA, either directly through genotoxins or indirectly by triggering inflammatory responses.
The Link Between Low Carb Diets and Cancer Risk
Mice in the study were fed different diets for nine weeks: low-carb, low-fiber, standard, and Western diets (high in fat and sugar). After the feeding period, the researchers monitored the development of polyps and tumors.
The study found that only mice on a low-carb diet combined with E. coli showed increased risk for colorectal cancer. This is significant because E. coli is found in about 60% of colorectal cancer cases. Mice on this combined diet developed more polyps and tumors, and showed DNA damage—markers of cancer development.
Low-carb diets were also found to thin the mucus layer in the colon, which normally acts as a barrier against harmful bacteria. In mice with E. coli, this thinning allowed a toxin called colibactin to reach the colon cells. Colibactin is known to damage DNA, contributing to cancer risk.
Additionally, mice on the low-carb, low-fiber diet with E. coli showed signs of gut health disruption, inflammation, and cell aging, all of which are linked to cancer development. The overall damage to the gut microbiome created an environment that supports the growth of colorectal cancer.
A Potential Solution: Fiber
Despite the alarming findings, the researchers discovered that adding fiber to the mice’s diet helped reduce tumor formation and control inflammation. This suggests that fiber may have a protective effect, even for those on low-carb diets.
The team plans to continue their research to determine whether specific types of fiber are more effective in preventing colorectal cancer. They also hope to study the impact of these findings on humans in the future.
This study highlights the need for more caution when considering low-carb diets, especially for those with a family history of colorectal cancer or other risk factors. As the research evolves, it could lead to new dietary recommendations to reduce cancer risk.
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