Does Dietary Fiber Improve Brain Function As We Age?

There’s a huge body of research into why cognitive and memory function seem to decline as we age. A number of mechanisms and age-related conditions have been identified as connected to this decline. One is chronic brain inflammation. The solution to that issue may be simpler than we knew.

One explanation for the loss or reduction of memory and other brain functions as we age is related to an immune cell present in mammalian brains called microglia. As we age, these cells become chronically inflamed, causing them to produce chemicals that impair motor function, memory and cognitive abilities.


But a 2018 study from the University of Illinois seems to have shown that we may be able stave off these cognitive and motor function issues with a common nutrient: dietary fiber.

It seems to revolve around butyrate, a short-chain-fatty-acid (SCFA) produced by good bacteria in the gut. Butyrate is produced when the bacteria eat the fiber.

“Butyrate is of interest because it has been shown to have anti-inflammatory properties on microglia and improve memory in mice when administered pharmacologically,” says Rodney Johnson, professor and head of the Department of Animal Sciences at U of I, and corresponding author on the Frontiers in Immunology study.


Previous studies have shown the positive effects on cognition and memory of sodium butyrate, which is the drug form of butyrate. However, the mechanism by which it worked remained unclear. The University of Illinois study showed that butyrate inhibits the production of damaging chemicals in inflamed microglia. Among these chemicals is interleukin (IL)-1β. Interleukin (IL)-1β has been shown to be a factor in human Alzheimer’s disease.

What the researchers wanted to find out, beyond knowing how the drug form of butyrate works, was if the same effects would result from just feeding the mice more fiber.


“People are not likely to consume sodium butyrate directly, due to its noxious odor,” Johnson says. “A practical way to get elevated butyrate is to consume a diet high in soluble fiber.”

The basis of the concept is the fact that gut bacteria naturally change fiber into butyrate.

“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, while diets high in fat and protein can have a negative influence on microbial composition and function. Diet, through altering gut microbes, is one way in which it affects disease,” says Jeff Woods, professor in the Department of Kinesiology and Community Health at U of I, and co-author on the study.


The theory was that butyrate derived from dietary fiber should be equally effective at reducing inflammation in micrioglia as sodium butyrate. This was the first time that theory was being put to the test.

The study involved two groups of mice – one young, one old. The mice were fed low- and high-fiber diets, Researchers then measured the levels of butyrate and other SCFA’s in the blood and levels of 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,” Johnson says. “It’s interesting that young adults didn’t have that inflammatory response on the same diet. It clearly highlights the vulnerability of being old.”

However, there was no difference between the age groups when fed the high-fiber diet. The intestinal inflammation among the older mice was reduced dramatically. Johnson concluded that, “Dietary fiber can really manipulate the inflammatory environment in the gut.”


After that, the researchers examined the mice for signs of inflammation in the brain. This involved looking at 50 unique genes in microglia. They concluded that the high-fiber diet reduced the inflammatory profile in the older mice.

While cognition, motor function and behavior were not directly studied here, more research of this nature is planned. It will be funded by a nearly $2 million grant from the National Institute of Aging, part of the National Institutes of Health.


Even though the study was not conducted on humans, Johnson believes the results are applicable, even if only in a general sense.

“What you eat matters. We know that older adults consume 40 percent 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.”


The list of benefits of dietary fiber is long and well studied. Now, it seems, we can add one more to that list: butyrate production by your gut bacteria and reduced inflammation in brain cells.

Your digestive tract will thank you for getting enough fiber in your diet. Apparently, so will your brain.

Keep the faith and keep after it!

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Journal Reference – Stephanie M. Matt, Jacob M. Allen, Marcus A. Lawson, Lucy J. Mailing, Jeffrey A. Woods, Rodney W. Johnson. Butyrate and Dietary Soluble Fiber Improve Neuroinflammation Associated With Aging in Mice. Frontiers in Immunology, 2018; 9 DOI: 10.3389/fimmu.2018.01832

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