Fiber's Cancer-Fighting Effect Depends on Gut Bacteria
Bacteria
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SAN DIEGO — A high-fiber diet may protect against colon cancer, but only if you have the right gut bacteria, a new study in mice suggests.

In the study, mice were fed either a low- or high-fiber diet, and some had a type of bacteria in their gut that ferments fiber into a chemical called butyrate, while others did not. All of the mice were then given a cancer-causing chemical so that they would develop colon tumors.

The number of tumors was 75 percent lower in mice that were fed a high-fiber diet and had the butyrate-producing bacteria in their guts, compared with the other mice. However, the high-fiber diet by itself, without the butyrate-producing bacteria, did not protect against colon cancer; nor did a low-fiber diet with butyrate-producing bacteria. [5 Diets That Fight Diseases]

"Our study shows that it's not the high fiber in and of itself that has a protective effect against cancer, but it’s a combination of the fiber plus having the right types of bacteria," said Scott Bultman, an assistant professor at the University of North Carolina School of Medicine, who presented the research here at the meeting of the American Association for Cancer Research.

The researchers noted that healthy colon cells use butyrate for fuel, but cancer cells do not (instead, they use the sugar glucose). Because cancer cells do not use butyrate, the chemical collects inside the cells, potentially causing them to self-destruct, Bultman said.

What about people?

The question of whether fiber protects against colon cancer in people has been controversial; some studies suggest a link between a high-fiber diet and a reduced risk of the disease, while others show no such link.

But these studies did not include information about gut bacteria, and it's possible that differences in people's gut bacteria affected the results, Bultman said.

While everybody likely has some gut bacteria that turn fiber into butyrate, some people have higher levels than others. In fact, several recent studies have found that healthy people have higher levels of butyrate-producing bacteria than people with colon cancer, Bultman said.

Future studies should look at people's diets, as well as their gut bacteria and genes, to determine whether there is a connection between a high-fiber diet with gut bacteria and a reduced risk of colon cancer, Bultman said.

Fortifying foods

Bultman noted that, for most people, eating a high-fiber diet naturally boosts the number of butyrate-producing bacteria.

But some genes that prevent people from increasing their levels of butyrate-producing bacteria, even with a high-fiber diet.

If studies confirm that butyrate protects against colon cancer in humans, then perhaps foods could be fortified with butyrate or butyrate-producing bacteria. This could be done for people whose guts do not naturally increase butyrate-producing bacteria, or those who don't like to eat fiber, Bultman said.

However, manufacturers would have to figure out a way to add butyrate to food, as the compound does not smell very good, Bultman said.

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