Before the switch, however, all of the participants underwent colonoscopies. A second procedure was performed at the end of the study period.
The researchers also assessed certain risk factors for colon cancer, including biological markers for the disease. And they examined bacteria samples taken from the participants’ colons.
When the study began, nearly 50 percent of those in the American group had polyps, or abnormal growths, in the lining of their colon. Although these growths are not harmful, they could eventually lead to cancer, O’Keefe’s team noted.
In contrast, none of the volunteers from South Africa had polyps upon entry to the study.
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After two weeks of eating the African diet, the American volunteers showed dramatic reductions in colon inflammation, the researchers said. They also showed declines in certain other signals tied to colon cancer risk.
On the other hand, colon cancer risk factors rose significantly among the Africans who made the switch to a high-fat, high-protein, low-fiber American-style diet, the team said.
“We can’t definitively tell from these measurements that the change in their diet would have led to more cancer in the African group or less in the American group, but there is good evidence from other studies that the changes we observed are signs of cancer risk,” study co-author Jeremy Nicholson of Imperial College London said in the news release.
The good news, he said, is that “people can substantially lower their risk of colon cancer by eating more fiber. This is not new in itself but what is really surprising is how quickly and dramatically the risk markers can switch in both groups following diet change.
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One possible explanation for the effects of diet on colon cancer risk is the way bacteria in the gut respond or adapt to the change, the researchers explained. For those in the American group, switching to a high-fiber diet led to increase in the production of butyrate, a byproduct of fiber metabolism that can help prevent cancer.
“The gut microbiome is being increasingly recognized as an important contributor to human health,” added Dr. James Kinross, a colorectal surgeon and a member of the research group at Imperial. “This research shows that gut bacteria are critically important for mediating the link between diet and colon cancer risk. This means we can look to develop therapies targeting gut bacteria as a way to prevent and treat cancer.”
According to the study authors, colon cancer is the fourth leading cause of death from cancer around the world, claiming more than 600,000 lives each year. Rates of colon cancer are much higher in the United States and other western nations than in Africa or the Far East.
The study was funded by the U.S. National Institutes of Health and the National Institute for Health Research Imperial Biomedical Research Centre in the United Kingdom.
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