Dietary fiber may reduce brain inflammation during aging

As mammals age, immune cells in the brain known as microglia become chronically inflamed. In this state, they produce chemicals known to impair cognitive and motor function. That’s one explanation for why memory fades and other brain functions decline during old age. But, according to a study published in Frontiers of Immunology, there may be a remedy to delay the inevitable: dietary fiber.

When dietary fiber is ingested, the bacteria in the gut convert it into short-chain-fatty-acids (SCFAs), including butyrate. The study reveals that in old mice butyrate inhibits production of damaging chemicals by inflamed microglia. One of those chemicals is interleukin-1β, which has been associated with Alzheimer’s disease in humans.

University of Illinois researchers were interested in knowing whether the same effects could be obtained simply by feeding the mice more fiber. The researchers fed low- and high-fiber diets to groups of young and old mice, then measured the levels of butyrate and other SCFAs in the blood, as well as inflammatory chemicals in the intestine.

“The high-fiber diet elevated butyrate and other SCFAs in the blood both for young and old mice. But only the old mice showed intestinal inflammation on the low-fiber diet,” said study author Rodney Johnson, professor and head of the Dept. of Animal Sciences at the University of Illinois. “It’s interesting that young adults didn’t have that inflammatory response on the same diet. It clearly highlights the vulnerability of being old.”

On the other hand, when old mice consumed the high-fiber diet, their intestinal inflammation was reduced dramatically, showing no difference between the age groups. The next step was looking at signs of inflammation in the brain. The researchers examined about 50 unique genes in microglia and found the high-fiber diet reduced the inflammatory profile in aged animals.

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