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Researchers at the University of Toronto have found that gut bacteria drive a common form of colon cancer, and that a low-carbohydrate diet can prevent the disease.

The researchers found that microbes in the intestine convert carbohydrates into metabolites that spur cancer growth. A low-carbohydrate diet shut down this process and led to a 75 per cent reduction in cancer incidence.

“Our results suggest that a diet low in carbohydrates could benefit those with a genetic predisposition to colon cancer,” said Alberto Martin, an associate professor in the Department of Immunology at U of T who holds the Canada Research Chair in Antibody Diversification.

“About 20 per cent of colon cancers thrive on mutations in genes involved in DNA mismatch repair. For this type of cancer, our study offers an explanation for the interplay among genetics, diet and intestinal microbiota,” said Martin.

No other research has explained the interaction of those three factors in colon cancer, although several studies have shown a link among them. As well, Martin and his team found that inflammation did not play a role in colon cancer, despite evidence from other studies that it promotes the disease.

The researchers did their study in mice, but with a low-carbohydrate, high-protein diet that humans could replicate. The results also provide a potential explanation for many studies in humans that have linked colon cancer to the “Western diet,” which is generally rich in complex carbohydrates such as pasta and bread, and in saturated fats from red meat and cheese.

In the Western world, about one in 15 people will get colon cancer. In Canada, the disease is the second-leading cause of cancer-related death, claiming about 5,000 lives a year.

Martin and his lab are now testing whether the low-carb diet could be an effective treatment in mice with advanced colon cancer, and are planning work with clinical researchers to see if a dietary change can improve outcomes for people with colon cancer.

The Martin lab is also experimenting with antibiotics as a potential treatment for colon cancer. “Our early research on this project showed that one metabolite in particular — butyrate — is a key driver of colon cancer, so it’s conceivable that antibiotics that limit butyrate could help prevent or control colon cancer,” said Martin. The lab is also looking at whether butyrate could be a biomarker for colon cancer risk.

The journal Cell published the study online. The research was funded by the Canadian Institutes of Health Research, the Cancer Research Society, the Lotte and John Hecht Memorial Foundation grant of the Canadian Cancer Society, and the Canada Research Chairs program.

Jim Oldfield is a writer with the Faculty of Medicine at the University of Medicine.