Though it's fairly a well-known fact that diets high in fiber help stave off colon cancer, the mechanism behind this has been largely unknown — until now. Researchers at the Medical College of Georgia have reported in this month's Cancer Research that butyrate, an end-product of the breakdown of fiber in the gut, acts as an anti-cancer agent in a couple of different ways.
A variety of bacteria live naturally and peaceably in our intestines. One of the authors of the study, Vadivel Ganapathy, jokes that the relationship is "like teenage kids in the house. We cohabitate; we provide them everything; but they don't do anything in return for us." But really, the relationship is quite beneficial to both parties: the bacteria get a place to live and free food, and we get help with digestion.
One area in which the bacteria are helpful is the breakdown of fiber. An end product of this process is the compound butyrate. The researchers in this study have found that one of the ways in which butyrate works to inhibit cancer growth is by binding to a specific receptor in the colon, GPR109A. Colon cancer also binds to GPR109A, but when butyrate beats the cancer to it, the receptor continues work, signaling the body's ability to kill cancer cells. At the same time, by binding to the GPR109A receptor, butyrate prevents the cancer from binding to the receptor and blocking this its action, which effectively prevents the cancer from becoming established.
In an earlier study, researchers at the Medical College found that butyrate is also moved inside the cell by a transporter gene, SLC5A8, where it can inhibit an enzyme that is critical to cancer cell growth. In the current study, the team found that in 15 out of 18 cancer patients, SLC5A8 was turned off in the colon. The team concludes that cancer cells are able to turn off the transporter, just as with the receptor.
"Colon cancer does not want butyrate produced by bacteria to come inside so it silences the transporter. It also does not want butyrate to act on the cell from the outside so it silences the receptor,"Ganapathy says. "It does not want to have anything to do with butyrate."
Apparently, high doses of butyrate are not very appetizing, but niacin is thought to have a similar effect on colon health, and is less aversive to the taste buds. Ganapathy plans to begin clinical trials comparing the effects of butyrate, niacin, and a high-fiber diet on colon cancer.