Many people cut carbs for health reasons, but new research suggests that this might actually harm their bodies.
A recent study by researchers at the University of Toronto’s Faculty of Medicine found that lab rats on low-carb diets had a higher occurrence of colon polyps.
The study focused on rats carrying specific gut bacteria linked to colon cancer development, including E. coli NC101, Bacteroides fragilis, and Helicobacter hepaticus. Notably, when combined with a low-carb diet, E. coli NC101 produced a DNA-damaging substance called colibactin. This substance was found to damage the colon lining and promote the formation of polyps.
E. coli NC101 is a bacterium found in 60% of colon cancer patients and 40% of individuals with bowel diseases, and it is also present in about 2 out of 10 generally healthy people. The researchers observed that rats on low-carb diets had thinner colon linings, and it is believed that colibactin could penetrate the weakened lining, promoting tumor growth in the colon.
The study identified a lack of fiber as a key factor in colon cancer development. While previous research pointed to high-fat and high-sugar diets as risk factors, this study surprisingly found that a typical Western diet doesn’t directly cause colon cancer. Instead, the low-carb diet weakens the colon’s protective lining.
Dr. Bhupesh Thakur, the study’s lead author, suggests that adding plenty of fiber to a low-carb diet could help mitigate these risks. Professor Alberto Martin, the study’s principal investigator, warns that while low-carb diets may be great for shedding pounds, they could have long-term health consequences.

The researchers warned that a low-carb diet could pose a greater risk to individuals with inflammatory bowel diseases such as ulcerative colitis, Behçet’s enteritis, and Crohn’s disease. These patients are more likely to carry E. coli NC101, which could increase the risk of developing colon cancer on a low-carb diet.
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