To learn more about colon cancer risks, researchers asked a few African Americans and South Africans to swap diets for two weeks.
While practicing in South Africa, principal investigator Stephen O’Keefe, a professor of medicine in the gastroenterology, hepatology, and nutrition division at the University of Pittsburgh School of Medicine, observed that his rural patients rarely had colon cancer or intestinal polyps, which can be a cancer precursor.
In the Western world, colon cancer is the second-leading cause of cancer death and African Americans carry the greatest disease burden in the United States.
“The African-American diet, which contains more animal protein, and fat, and less soluble fiber than the African diet, is thought to increase colon cancer risk,” O’Keefe says. “Other studies with Japanese migrants to Hawaii have shown that it takes only one generation of Westernization to change their low incidence of colon cancer to the high rates observed in native Hawaiians.
“In this project, we examined the impact of a brief diet change on the colon in a controlled setting where we didn”t have to worry about the influence of smoking and other environmental factors on cancer risk.”
After assessment of their in-home diets, 20 African-American and 20 rural South African volunteers ages 50 to 65 spent two weeks at a University of Pittsburgh site and at an African lodging facility respectively, where they ate meals prepared by the researchers using ingredients and cooking techniques typical of the other group.
The team examined fecal and colon content samples, obtained during colonoscopy, of each volunteer at baseline and after the two-week study period. Their findings are published inNature Communications,
Signs of Cancer Risk
Although the diet change was brief, each group took on the other’s rates of turnover of cells of the intestinal lining, levels of fiber fermentation, and markers of bacterial metabolic activity and inflammation associated with cancer risk.
In particular, African Americans experienced an increase in butyrate production, which is thought to play a key role in anti-cancer pathways. The researchers also noted they removed intestinal polyps from nine of the African-American volunteers, but none were present in the Africans.
“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,” says coauthor Jeremy Nicholson, of Imperial College London.
Increasing the amount of fiber in the diet—from approximately 10 grams to more than 50 for African Americans in the diet swap—likely led to biomarker changes reflecting reduced cancer risk, but eating less animal fat and proteins also could be helpful.
“These findings are really very good news,” Nicholson says. “In just two weeks, a change in diet from a Westernized composition to a traditional African high-fiber, low-fat diet reduced these biomarkers of cancer risk, indicating that it is likely never too late to modify the risk of colon cancer.”
Other researchers from the University of Pittsburgh and Imperial College London and from Wageningen University, University of Helsinki, University of Illinois, and the University of KwaZulu-Natal are coauthors of the study.
The National Institutes of Health the National Institute for Health Research Imperial Biomedical Research Centre, the Academy of Medical Sciences, the Spinoza Award of the Netherlands Organization for Scientific Research, the European Research Council, and the Academy of Finland funded the work.