Principal investigator Stephen O’Keefe, M.D.,
professor of medicine, Division of Gastroenterology, Hepatology and
Nutrition, Pitt School of Medicine, observed while practicing in South
Africa 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,” Dr. O’Keefe explained. “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 were housed at a
University of Pittsburgh site and at an African lodging facility
respectively. There 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.
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,” said
co-author Jeremy Nicholson, Ph.D., of Imperial College London.
According to Dr. O’Keefe, 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,” he said. “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.”
The team included other researchers from the University of
Pittsburgh and Imperial College London, as well as Wageningen University
in the Netherlands; University of Helsinki, Finland; University of
Illinois; and the University of KwaZulu-Natal in South Africa.
Funding for the study was provided National Institutes of Health
grants CA135379, RR024153 and TR000005; the National Institute for
Health Research Imperial Biomedical Research Centre, UK; the Academy of
Medical Sciences; the Spinoza Award of the Netherlands Organization for
Scientific Research, the European Research Council and the Academy of
Finland.