As all mammals age, microglia which are immune cells in the brain become chronically inflamed. When this occurs, they produce chemicals which can impair cognitive and motor functions. This is one explanation in regards to why the memory can fade and brain functions also decline during the aging process. According to a study at the University of Illinois College of Agricultural, Consumer and Environmental Sciences however, there might be a way to delay this inevitability and that is with dietary fiber.
Consuming dietary fiber will promote the growth of the good bacteria in the gut. As these bacteria digest ingested fiber, they produce SCFAs (short chain fatty acids) which includes butyrate, as byproducts. Butyrate is of particular interest as it has been shown to produce antiinflammatory properties on microglia. It has also been shown to improve memory in mice when it has been administered pharmacologically.
In previous studies, butyrate in drug form (sodium butyrate) showed positive outcomes although the mechanism wasn’t clear. The new study however reveals in old mice that butyrate inhibits the production of damaging chemicals produced by inflamed microglia. One of these damaging chemicals has been associated with Alzheimers disease in humans.
Researchers have been interested in how sodium butyrate works, however they are more interested in knowing whether similar effects can be obtained by feeding mice more fiber. People are highly unlikely to consume sodium butyrate due to its noxious odor, however a more practical way to get elevated butyrate is by consuming a diet high in soluble fiber. The idea goes directly to the fact that gut bacteria naturally convert fiber to butyrate.
Diet has a major influence on the function and composition of microbes found in the gut. Diets high in fiber benefit these good microbes. Diets high in fat and protein on the other hand, can have a negative influence on microbial function and composition. It was believed that butyrate which is derived from dietary fiber would have the same benefits in the brain as the drug form, sodium butyrate. However, it had not been previously tested. The research team fed low and high fiber diets to groups of both young and old mice. They then measured the levels of butyrate and other SCFAs contained in the blood and additionally, inflammatory chemicals in the intestine.
The diet high in fiber elevated butyrate and SCFAs in the blood in both the young and old mice. However, only the old mice showed intestinal inflammation on the low fiber diet. The young adult mice did not have the inflammatory response on the same low fiber diet as the old mice. This indicates the vulnerability of the aging process and diet. When the old mice were fed the high fiber diet, the intestinal inflammation was drastically reduced revealing that dietary fiber can manipulate the inflammatory environment in the gut.
The next step the researchers took was to look at signs of brain inflammation. They examined about 50 unique genes in microglia and discovered that high fiber diet reduced the inflammatory profile in older mice.
The next step for the researchers is to examine the effects of diet on behavior and cognition and the precise mechanisms in the gut brain axis. Although the current study was conducted on mice, the team is comfortable in extending the finding to humans if only in a general way. What we eat matters and it is known that older adults consume 40% less dietary fiber than is recommended. By not consuming enough fiber, negative consequences can occur. Most people do not make the connection to brain health and inflammation in general.
To view the original scientific study click here: Butyrate and Dietary Soluble Fiber Improve Neuroinflammation Associated With Aging in Mice. Frontiers in Immunology, 2018; 9 DOI: 10.3389/fimmu.2018.01832