By Jasminee Sahoye
A group of researchers have discovered that when they switched diets for American and African volunteers in their study, there was a big effect on risk factors for colon cancer.
In their quest to find out about diet and gut bacteria, an international team including scientists from the University of Pittsburgh and Imperial College London carried out a study with 20 African American volunteers and a group of 20 participants from rural South Africa. The two groups swapped diets under tightly controlled conditions for two weeks.
The volunteers had colonoscopy examinations before and after the diet swap. The researchers also measured biological markers that indicate colon cancer risk and studied samples of bacteria taken from the colon.
At the start, when the groups had been eating their normal diets, almost half of the American subjects had polyps – abnormal growths in the bowel lining that may be harmless but can progress to cancer. None of the Africans had these abnormalities.
After two weeks on the African diet, the American group had significantly less inflammation in the colon and reduced biomarkers of cancer risk. In the African group, measurements indicating cancer risk dramatically increased after two weeks on the Western diet.
Western diets, high in protein and fat but low in fibre, are thought to raise colon cancer risk compared with African diets, high in fibre and low in fat and protein.
This new study, confirms that a high fibre diet can substantially reduce risk and shows that bacteria living in the gut play an important role in this effect.
Colon cancer is the fourth commonest cause of death from cancer worldwide, accounting for over 600,000 deaths per year. Colon cancer rates are much higher in the Western world than in Africa or the Far East, yet in the U.S., African Americans shoulder the greatest burden of the disease.
Team lead, Prof. Jeremy Nicholson of the Department of Surgery and Cancer at Imperial College London, 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.
“The findings suggest that people can substantially lower their risk of colon cancer by eating more fibre. 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.
“These findings also raise serious concerns that the progressive westernization of African communities may lead to the emergence of colon cancer as a major health issue.”
Prof. Stephen O’Keefe at the University of Pittsburgh, who directed the study, said: “Studies on Japanese migrants to Hawaii have shown that it takes one generation of westernization to change their low incidence of colon cancer to the high rates observed in native Hawaiians.
“Our study suggests that westernization of the diet induces changes in biomarkers of colon cancer risk in the colonic mucosa within two weeks. Perhaps even more importantly, a change in diet from a westernized composition to a ‘traditional African’ high-fibre low fat diet reduced these biomarkers of cancer risk within two weeks, indicating that it is likely never too late to change your diet to change your risk of colon cancer.”
The study found that a major reason for the changes in cancer risk was the way in which the bacteria in the gut – known as the microbiome – altered their metabolism to adapt to the new diet. In the American group, the researchers found that the African diet led to an increase in the production of butyrate, a by-product of fibre metabolism that has important anti-cancer effects.