Fiber is a key element of a healthful diet. New research breaks down the mechanism by which it can delay age-related brain inflammation.

If all the studies that urge people to consume a diet rich in fruits, vegetables, and whole grains for a healthy life haven't convinced you yet to add more broccoli to your plate, perhaps this latest research will.

Eating fiber-rich foods—such as broccoli, nuts, oats, beans, and whole-grain bread—might help delay brain aging by triggering the production of a short-chain fatty acid that has anti-inflammatory properties.

This the main takeaway of a new study that was recently published in the journal Frontiers in Immunology.

Rodney Johnson, a professor and the head of the Department of Animal Sciences at the University of Illinois at Urbana-Champaign, is the corresponding author of the study, and Stephanie M. Matt is the first author of the paper.

How fiber lowers inflammation

As Matt and colleagues explain in their study paper, microglia—a major type of immune cell in the brain—tend to become hyperactive and chronically inflamed with age. This inflammation of the microglia is one of the main causes of memory and cognitive decline in old age.

Previous research has shown that a drug form of butyrate, which is a short-chain fatty acid that is produced in the colon when bacteria ferment fiber in the gut, can improve memory and reduce inflammation in mice.

However, the precise mechanisms behind this weren't entirely understood. Also, previous research had not shown whether simply increasing the dietary content of fiber would achieve the same results as the drug.

So, Matt and colleagues fed young and aging mice diets high and low in fiber. Then, the scientists measured the mice's blood levels of butyrate and their levels of pro-inflammatory substances in their intestines.

Professor Johnson sums up these findings, saying, "The high-fiber diet elevated butyrate and other [short-chain fatty acids] in the blood both for young and old mice."

"But," he goes on, "only the old mice showed intestinal inflammation on the low-fiber diet [...] It's interesting that young adults didn't have that inflammatory response on the same diet. It clearly highlights the vulnerability of being old."

Also, consuming a high-fiber diet reduced the intestinal inflammation in aging mice so much that it was indistinguishable from that of young mice.

"Dietary fiber can really manipulate the inflammatory environment in the gut," says Professor Johnson. What about the brain, however?

Why fiber is good for your brain

A genetic analysis of inflammatory markers conducted by the scientists found that a high-fiber diet reduced inflammation in the brain's microglia. The researchers suspect that this was achieved by diminishing the production of a pro-inflammatory chemical known as interleukin-1β, which some studies have linked with Alzheimer's.

Study coauthor Jeff Woods, a professor in the Department of Kinesiology and Community Health at the University of Illinois at Urbana-Champaign, comments on the findings.

"We know that diet has a major influence on the composition and function of microbes in the gut and that diets high in fiber benefit good microbes," he points out, "while diets high in fat and protein can have a negative influence on microbial composition and function."

Altering gut microbes, explains Professor Woods, "is one way in which [diet] affects disease."

Professor Johnson explains that the findings are relevant to humans, saying, "People are not likely to consume sodium butyrate directly, due to its noxious odor," he says, but, "A practical way to get elevated butyrate is to consume a diet high in soluble fiber."

"What you eat matters. We know that older adults consume 40% less dietary fiber than is recommended. Not getting enough fiber could have negative consequences for things you don't even think about, such as connections to brain health and inflammation in general."

Professor Rodney Johnson