Low-carbohydrate diets, such as the ketogenic diet, are often praised for their effects on weight loss. But a recent study reveals that they could promote the development of colorectal cancers by altering the balance of gut bacteria.
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Researchers from the University of Toronto explored the interactions between diet and gut microbiota. Their work, published in
Nature Microbiology, shows that a diet low in carbohydrates and soluble fibers promotes the proliferation of toxin-producing bacteria, thereby increasing the risks of colorectal cancer.
The key role of gut bacteria
The study focused on comparing three types of diets: normal, low-carbohydrate, and Western (high in fats and sugars). Mice fed a low-carbohydrate diet and carrying a specific strain of E. coli naturally present in the human gut developed more polyps and tumors. This combination created an environment conducive to the proliferation of harmful bacteria, particularly those producing toxins such as colibactin.
These polyps, although often benign, can evolve into cancers. The researchers observed that the combination of a low-carbohydrate diet and the presence of colibactin-producing E. coli, a toxin that damages DNA, accelerated this process. Colibactin also weakens the intestinal mucus barrier, exposing colon cells to genetic damage.
In the absence of soluble fibers, the balance of the gut microbiota is disrupted. Beneficial bacteria decrease, while pathogenic strains, such as certain E. coli, proliferate. This dysbiosis promotes inflammation and tumor formation, highlighting the importance of a balanced diet to maintain a healthy microbiota.
The protective impact of fibers
Soluble fibers, found in vegetables, fruits, and legumes, play an important role in protecting the intestinal mucosa. The study showed that reintroducing them into the diet of mice reduced inflammation and the number of tumors. These fibers act as a shield by strengthening the mucus barrier, thus limiting the access of bacterial toxins to colon cells.
The researchers also observed that soluble fibers alter the composition of the gut microbiota. They promote the growth of beneficial bacteria, which produce short-chain fatty acids, essential for gut health. These compounds reduce inflammation and maintain the integrity of the intestinal wall, preventing the proliferation of pathogenic bacteria.
Finally, soluble fibers seem to inhibit the production of colibactin by certain strains of E. coli. By feeding beneficial bacteria, they create an environment less conducive to pathogens. This discovery underscores the importance of a fiber-rich diet to prevent intestinal diseases, including colorectal cancer.
Article author: Cédric DEPOND