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Study's food swap confirms risks of colon cancer

May 11, 2015


When African-Americans and rural South Africans swapped diets for two weeks, they also swapped risk factors for colon cancer. And the surprise is that it happened so quickly.

The swap involved 20 African-Americans who ate South African fare including cornmeal and beans for two weeks, while 20 South Africans consumed an American diet full of meat protein and fats, including fast-food burgers and chicken. The South African diet consisted of one-sixth the meat of the American diet.

A University of Pittsburgh-based study published online in Nature Communications found that the South African cornmeal-bean diet reduced risk factors for colon cancer, including changes in gut flora and reductions in inflammation in colon’s mucosa in the American group, while the American diet notably increased the Africans’ risk factors for colon cancer.

The study, involving an international research team, confirms that dietary fiber alone reduces inflammation and blocks secondary bile in the colon, cutting the cancer risk. The South African diet reduced levels of secondary bile in the colon by 70 percent.

But that same carcinogenic bile increased in South Africans on the American diet by 400 percent, the study found.

The plant-based, high-fiber African diet also elevated levels of butyrate, a molecule that reduces inflammation levels and cancer biomarkers.

"If you can increase the amount of (butyrate), you can override the carcinogenic effects of fat and meat," said lead author Stephen J.D. O’Keefe, a physician in the Division of Gastroenterology, Hepatology and Nutrition in Pitt’s School of Medicine.

The plant-based South African diet is considered a factor in that nation’s colon-cancer rate of only five people per 100,000 population, as compared with the African-American colon cancer rate of 65 per 100,000 — a rate 13 times greater among African-Americans.

All 40 participants were provided food in measured quantities and received biopsies of colon mucosa before and after the study. Each of the 40 participants also underwent colonoscopies, with regular testing for healthful and colon-cancer biomarkers in the urine and feces.

"These findings are really very good news," Dr. O’Keefe 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 study didn’t last long enough to produce changes in cholesterol and blood pressure, he said.

While such studies won’t likely change eating habits, "our best hope is that it will open eyes to other possibilities, and point to the fact that a high-fiber diet is not difficult to follow and is well tolerated," Dr. O’Keefe said. "It is enjoyable to eat good food."

Michael Greger of NutritionFacts.org said "studies like this show that diet can trump genes when it comes to some of our most common cancers."

Joel Kahn, a clinical professor of medicine at the Wayne State University School of Medicine in Detroit, said the study represents "sophisticated science."

"We have learned that changes in dietary patterns have profound influences that occur very quickly," he said, citing two other studies that used plant-based diets to reduce angina within two weeks and lead to prostate-cancer suppression in three months.

"I think the message here is that this is further evidence that food is information and food speaks directly to genes about the risks of diabetes, heart disease, cancer and obesity, and it doesn’t take long to do this," Dr. Kahn said.

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