Most colon cancers are believed to be due to diet. The authors of this study speculate that products of the metabolism of food by the colon microbiome determine the risk of colon cancer. Dietary patterns can change cancer risk, and diets rich in fresh fruit, vegetables, fiber, antioxidants, calcium, and vitamin D reduce the risk of cancer. Diets high in red meat and saturated animal fats increase the risk of cancer.
Africans rarely get colon cancer, but African Americans are at great risk of developing colon cancer. According to the authors consumption of large amounts of red meat may be responsible for the high colon cancer risk in African Americans. The diet high in maize (corn) meal and low in animal fat may be the cause of the low risk in Africans.
Short chain fatty acid (SCFA) butyrate is known to promote colon health and is the preferred energy source for colon bacteria. Bacteria in the healthy colon produce butyrate and vitamins such as folate and biotin. Therefore, the authors studied the metabolism of colon bacteria of high-risk and low-risk populations for comparison. (The subjects were recruited from Pittsburgh, Pennsylvania, and Pretoria, South Africa.)
Participants ate their normal diets. They were given a colonoscopy preparation liquid, and their colon contents were collected and studied in the lab. The colon contents were studied for SCFA, vitamins, and minerals. Calcium and iron were highest in Caucasian Americans, and zkinc was higher in African Americans than in other groups. Butyrate, acetate, and propionate (the 3 major SCFAs) were higher in Africans than in African Americans or Caucasian Americans. SCFAs were similar between African Americans and Caucasian Americans. Colonic folate was not lower in Africans in spite of their lower dietary intake of folate as were their biotin levels.
Butyrate is not found in our diets, but is produced by specific colon bacteria from fiber and resistant starch. The group with the lowest cancer risk, Africans, had the highest butyrate levels. From 10 to 20 percent of resistant carbohydrate passes through the small intestine and is found undigested in the colon. Increased amounts of carbohydrate in the colon results in the production of more folate by the microbiota. Fructo-oligosaccharide (FOS), a prebiotic, acts as a resistant starch and helps produce more folate.
CONCLUSION: The results of this study support the hypothesis of the authors that colon health is mediated by SCFAs produced in the colon by bacteria, especially butyrate.
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PMID: 19741203.
Summary #738.
