Research shows why African Americans get more colon cancer than Native Africans
Study suggests high-meat diets encourage "bad" bacteria in the gut
Washington--In a paper presented this morning at the International Research Conference of the American Institute for Cancer Research (AICR), Dr. Stephen J. O’Keefe of the University of Pittsburgh reported on his AICR-funded research into colon cancer among African Americans.
Dr. O’Keefe and his colleagues sought to understand why only 1 in 100,000 Native Africans get colorectal cancer, compared to 1 in 2,000 African Americans.
"Our research suggests that higher colon cancer rates seen among African Americans may be due to diets high in animal protein and fat. There is good experimental evidence to support the hypothesis that such diets encourage specific kinds of intestinal bacteria to flourish.
"These bacteria produce by-products that injure the cells lining the colon and increase the risk of developing cancer," Dr. O’Keefe said.
Over 400 different species of intestinal bacteria or "gut flora" are living inside us, O’Keefe said, and the foods we eat determine the ratio of "good" to "bad" gut flora by allowing some kinds to out-compete others. Eating a diet high in animal protein and fat is likely to cause two kinds of gut flora to increase:
o Sulfur-reducing bacteria, whose growth is stimulated by the high sulfur content of meat. These bacteria produce hydrogen sulfide that is toxic to colon cells.
o 7-alpha-dehydroxylating bacteria, whose growth is stimulated by bile acids the body synthesizes in response to fat in the diet. These bacteria convert bile acids into secondary forms, which are carcinogenic in experimental models.
Over time, O’Keefe said, the continued presence of these substances in the gut increases the odds of cancer in cells lining the colon.
Diets low in meat and fat, and high in carbohydrate, encourage other kinds of bacteria to flourish in the gut--methanogenic bacteria that produce non-toxic methane.
By focusing on how diet influences gut flora, Dr. O’Keefe’s study is an example of research that is linking overall dietary patterns, not specific foods or food supplements, to cancer risk.
"It’s what you eat most of the time--your typical diet over months and years--that influences, which gut flora thrive," he said. "Looking at gut flora gives us an ‘in,’ a way to evaluate how individuals are eating most of the time."
According to government statistics, (the Continuing Survey of Food Intakes by Individuals or CSFII), African Americans eat 77 pounds of beef per person per year, significantly more than both Hispanic Americans (69 pounds) and Caucasian Americans (65 pounds). African Americans also consume much more pork (63 pounds) per year than Hispanics (45 pounds) and whites (49 pounds).
In his AICR-funded study, Dr. O’Keefe and his colleagues compared the recalled three-day dietary intake, colon biopsies and gut flora of 17 Native Africans and 18 African Americans.
Native Africans, who said they ate a staple diet high in corn meal (carbohydrate) and low in animal meat and fat, had more of the "good" methanogenic bacteria and Lactobacilli planatarum, a bacterium that has been shown to help protect the lining of the colon from the kind of damage that can spark cancer. Polyps were found in only one Native African subject.
African Americans ate more meat and fat and had more 7-alpha-dehydroxylating bacteria; colon polyps were found in 7 out of 18 African American subjects.
"This study supports the theory that diets high in meat and fat alter colonic flora, encouraging the growth of bacteria that produce a chronic inflammatory condition in the lining of the colon," Dr. O’Keefe said.
"There is increasing experimental evidence that chronic inflammation stimulates mucosal growth and increases the exposure of the rapidly dividing cells lining the gut to other environmental carcinogens'
Dr. O’Keefe, a Professor of Medicine in the Division of Gastroenterology, Hepatology and Nutrition at the University of Pittsburgh, is currently chair of the Nutrition and Obesity Section of the American Gastroenterological Association.
His focus on the issue of colon cancer in African Americans began when he moved to the US from Cape Town, South Africa.
In Africa, Dr. O’Keefe clinical and research interests were nutrition and gastroenterological diseases in underdeveloped countries.
Upon moving to Richmond, Virginia, he noted that colonoscopies of African Americans were turning up many more adenomas (colon polyps, which can become malignant and lead to cancer) than he ever saw among Native Africans.
Dr. O’Keefe presented his research at the annual research conference of the American Institute for Cancer Research and World Cancer Research Fund in Washington, DC.
The AICR/WCRF International Research Conference of Food, Nutrition and Cancer is the world’s premier forum on the diet-cancer connection.
Other research presented at the two-day conference examined the roles of exercise, fiber, chronic inflammation, vitamin C, soy, and host of other dietary factors.
Panels also focused on the issue of diet in cancer survivorship, and the technologies that are allowing researchers to investigate how diet influence patterns of gene activity in cancer cells. |
