“Eat more fiber” is dietary advice that’s earned the right of repetition. High-fiber diets are linked to lower rates of heart disease and certain types of cancer, along with the daily bonus of keeping our digestive system running efficiently.
New research suggests another potentially big benefit: high-fiber diets may set off a chemical cascade resulting in reduced brain inflammation, which in turn could mean less cognitive decline and memory loss with age, and decreased risk of neurodegenerative diseases.
This was a mouse study, so it carries the caveat of “not yet tested in humans” – but as an initial look into the fiber-brain connection, the results are important.
Researchers started in the intestines by focusing on a short-chain fatty acid called butyrate, which is produced by bacteria that ferment fiber in the gut. Previous research found that a drug form of butyrate reduced tissue inflammation in mice and boosted the rodents’ memory. To find out if a diet high in fiber would have similar effects to the drug form of butyrate, the researchers fed young and aging mice high- and low-fiber diets and then tested their butyrate blood levels and assessed their levels of intestinal inflammation.
The results showed that a high-fiber diet delivered effects comparable to the drug by elevating butyrate and other short-chain fatty acids in both the young and old mice. The researchers noted that the high-fiber diet lowered intestinal inflammation in the older mice to levels indistinguishable from the young mice (which says a lot for the effects of a high-fiber diet even apart from other benefits).
Next, the researchers ran a genetic test on the mice and found that those fed a high-fiber diet also had reduced inflammation in their brain’s immune cells, known as microglia, which account for about 15% of all cells in the brain. Inflammation in microglia is thought to be one of the chief causes of cognitive decline as we age.
The researchers think this benefit came from the process that began with eating a high-fiber diet eventually reducing an inflammatory chemical known as interleukin-1β, which previous studies have linked to Alzheimer’s disease.
So the summary of the process revealed by this study looks like this: eating a high-fiber diet resulted in more short-chain fatty acids in the gut, including butyrate, which reduced intestinal inflammation, with the eventual effect of reducing brain-tissue inflammation. Reduced brain inflammation is linked to less cognitive decline and lower risk of dementia with age.
If these effects hold true in humans, the imperative to eat more fiber from sources like fruits, vegetables, nuts, seeds, beans and whole grains will be even more vital, particularly for older adults. And the results further reinforce a finding that’s turning up in study after study: what’s healthy for the heart is also generally healthy for the brain, and reducing inflammation is critically important for both.
“What you eat matters,” said corresponding study author Rodney Johnson, head of the Department of Animal Sciences at the University of Illinois at Urbana-Champaign. “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.”