Written by Marcia J. Egles, MD. Study shows how switching to a high-fiber, low-fat diet typical of rural Africans reduced gut inflammation and improved fiber digestion and risk markers for colon cancer in participating African Americans. 

How important is diet to the risk of colon cancer? Researchers from the University of Pittsburgh extensively examined data from of a group of African-Americans who switched to a traditional African diet for two weeks compared to a group of rural Africans who switched to an American diet for two weeks. The results may help explain the high numbers of colon cancer in African-Americans (65 cases yearly per 100,000 persons) as compared to the low occurrence of colon cancer in rural, black South Africans (less than 5 cases per 100,000 persons) (1).

Twenty healthy African Americans, and twenty healthy, black, rural South Africans were matched by age and gender in a two-week, highly supervised, dietary exchange program. The participants were men and women ages 50-65 years. Each person underwent laboratory tests including fecal analysis, as well as colonoscopies with biopsies at the start and after the conclusion of the two weeks.

The African-Americans were housed at a University of Pittsburgh site where they dined exclusively on African-style food prepared according to the specifications of the research staff. The African- Americans’ daily intakes of fiber increased from about 10 grams per day to 50 grams per day. They ate two to three times less animal fat and animal protein, more fish, and larger amounts of fruit and vegetables than their usual diets. Whereas their American diet had included many fried foods, the African diet used boiling as a major mode of food preparation.

The black South Africans were housed in an African lodge where they exclusively received foods typically eaten by their counterparts in Pittsburgh. They received a high fat, low fiber, western style diet complete with burgers and fries for two weeks. Both groups received in general the same number of calories of food, and both groups were only allowed to eat the food provided in the experiment.

At baseline, there were several notable differences between the two groups. Intestinal polyps were present in the African-Americans, but none were found among the Africans. No intestinal parasites were detected in the African-Americans, but two cases of schistosomiasis and one tapeworm segment were noted at baseline in the Africans.

Despite the short study length of the trial, the dietary changes for both groups resulted in major changes in the appearance of the intestinal mucosa, changes in the intestinal bacterial flora (4), and changes in several biochemical markers of cancer risk. These changes were reciprocal between the two groups with the African- American showing improvements with lessening of inflammation and improved levels of fiber fermentation products including increased butyrate levels, similar to the baseline of the Africans. Butyrate has been shown in other studies to be anti-inflammatory and anti-neoplastic (2, 3). The Africans, however, saw an unfavorable reversal in all the parameters, with a lessening of their butyrate levels in colonic evacuates by one-half as compared to baseline.

In addition to differences related to fiber consumption, the researchers also found differences related to dietary fat and its effects on gut bacteria. Their prior studies (5) had noted that higher fat diets are associated with greater deconjugation of bile acids through a mechanism involving bacterial genes. Such bile acids have been associated with increases in colon cancer risks in prior studies. (6,7). The current study was able to demonstrate  reductions in these bile acids as well as reductions in the bacterial bile acid-deconjugators in the African-Americans, and reciprocal increases among the Africans on the higher fat diet (1).

The results provide evidence for an influence of fiber and butyrate on intestinal mucosal health. An increase in fiber consumption, together with a moderation in fat intake, may constitute a strategy by which the high incidence of colon cancer in African-Americans, and other westerners, might be reduced. These observations would need to be confirmed by longitudinal studies to see if cancer rates could be reduced by such dietary changes.

Source: O’Keefe, Stephen JD, et al. “Fat, fibre and cancer risk in African Americans and rural Africans.” Nature communications 6 (2015).

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Posted July 13, 2015.

Marcia Egles, MD, graduated from Vanderbilt University School of Medicine in 1986.  She completed her residency in Internal Medicine at St. Louis University Hospital. Dr. Egles is certified in Internal Medicine and is a member of the American College of Physicians. She resides in Avon, IN with her husband and two sons.

References:

  1. O’Keefe, Stephen J.D. et al in Nature Communications, volume 6, 28 April 2015. doi:10.1038/ncomms7342
  2. Greer, J. B. & O’Keefe, S. J.Microbial induction of immunity, inflammation, and cancer. Front. Physiol.1, 168 (2011).
  3. Vipperla, K. & O’Keefe, S. J.The microbiota and its metabolites in colonic mucosal health and cancer risk. Nutr. Clin. Prac.27, 624–635 (2012)
  4. David, L. A.et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature 505, 559–563 (2014).
  5. Wells, J. E. & Hylemon, P. B.Identification and characterization of a bile acid 7α-dehydroxylation operon in Clostridium sp. strain TO-931, a highly active 7α-dehydroxylating strain isolated from human feces. Appl. Environ. Microbiol. 66, 1107–1113 (2000).
  6. Wells, J. E. & Hylemon, P. B.Identification and characterization of a bile acid 7α-dehydroxylation operon in Clostridium sp. strain TO-931, a highly active 7α-dehydroxylating strain isolated from human feces. Appl. Environ. Microbiol. 66, 1107–1113 (2000).
  7. Bernstein, C.et al. Carcinogenicity of deoxycholate, a secondary bile acid. Arch. Toxicol. 85, 863–871 (2011).