People who consume a high-fiber, low-fat diet modeled on eating habits in Africa can sharply reduce their risk for developing colorectal cancer—and quickly—a new study suggests.

Biomarkers linked to the risk for colorectal cancer changed significantly within two weeks of starting the strict dietary intervention—changing for the better on the “African” diet, while changing for the worse in the setting of a traditional American diet.

“The phenotype changes dramatically,” said Stephen J. O’Keefe, MD, MSc, professor of medicine at the University of Pittsburgh, who reported the findings at the 2015 Digestive Disease Week. The study also appeared in Nature Communications (2015;6:6342).

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The investigators said the findings may help explain why native Africans have a substantially lower risk for colorectal cancer than African Americans. Data show that the rate of colorectal cancer among African Americans is 65 cases per 100,000 people, compared with about five per 100,000 among native Africans.

The study was a two-week “food exchange” in which African Americans consumed a high-fiber, low-fat African-style diet consisting largely of boiled cornmeal and rural South Africans received a high-fat, low-fiber Western-style diet, such as hamburgers and french fries. The Western diet typically contains two to three times more fat and protein than an African diet, Dr. O’Keefe noted.

The dietary intervention consisted of a switch to a low-fat (mean, 51 g per day), high-fiber (mean, 55 g per day) diet for the African Americans, and for the native Africans a switch to a high-fat (mean, 123 g per day), low-fiber (mean, 7 g per day) diet.

“We were absolutely amazed to see the magnitude of changes at the mucosal level. We know the microbiome is very sensitive to dietary changes, but we did not know what this was doing to the mucosa,” Dr. O’Keefe said. “We believe that the 55 g per day of fiber is the key number. If it was 35 g per day, we may not have seen a positive result.”

African Americans also had greater expression of genes responsible for butyrate production and greater production of the gene product, short-chain fatty acids, which may reduce the risk for cancer. These substances decreased in the native Africans, while secondary bile acids—which may raise the risk for cancer—increased by 400%, according to the researchers.

Dagfinn Aune, MS, a research associate at Imperial College, London, and a doctoral student in nutritional epidemiology at the Norwegian University of Science and Technology, in Trondheim, called the study “very interesting” and said it provided “further biological clues to how dietary factors may influence colon cancer risk.”

Mr. Aune was first author of a recent meta-analysis looking at the effect of diet on the risk for prostate cancer (Am J Clin Nutr 2015;101:87-117).

“In migration studies, we have seen that Asians who move to the United States take on the colon cancer rates of their American neighbors within a generation,” Mr. Aune said. “In secular trend studies, we also see rapid increases in colon cancer rates in countries where dietary habits are becoming more westernized. Although colon cancers take years to develop, the current study suggests that biomarkers of colon cancers risk can be altered rather quickly with a mostly plant-based diet.”

—Caroline Helwick



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