Dietary fibre could be key to prevent age related decline in brain functions

Researchers from the University of Illinois suggest that dietary fibre could delay fading memory and the decline of other brain functions with age.

Immune cells, known as microglia, become chronically inflamed as mammals age. When they are inflamed, they produce chemicals known to impair motor and cognitive function – one explanation of why memory fades in old age. One chemical produced is interleukin-1β, which has been previously associated with Alzheimer’s disease.

Dietary fibre promotes the growth of good bacteria in the gut, and when these bacteria digest fibre, they produce SCFAs; short chain fatty acids, including butyrate, as byproducts.

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

Positive outcomes of the drug form of butyrate have been identified in previous studies, however the mechanism of how it works was not clear. This study found that in old mice, butyrate inhibits the production of damaging chemicals by inflamed microglia. 

The researchers wanted to identify whether the effects would be seen by feeding the mice more fibre, as the gut naturally converts fibre into butyrate.

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

To test their hypothesis, the researchers fed low- and high-fibre 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-fibre 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-fibre diet,” Prof Johnson said. “It’s interesting that young adults didn’t have that inflammatory response on the same diet. It clearly highlights the vulnerability of being old.”

The team also found that high-fibre diets reduced the inflammatory profile in aged mice. Despite the study being conducted in mice, the team are comfortable extrapolating their findings to humans. 

Prof Johnson concluded: “What you eat matters. We know that older adults consume 40 percent less dietary fibre than is recommended. Not getting enough fibre could have negative consequences for things you don’t even think about, such as connections to brain health and inflammation in general.”

The team have received almost $2 million as a grant from the National Institute on Aging to tackle further work on the effect of diet on cognition and behaviour, and the precise mechanisms in the gut-brain axis.

The study was published in Frontiers in Immunology.