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As mammals get older, immune cells in the brain, called microglia, become chronically inflamed. In this state, they produce chemicals known to impair cognitive and motor functions. This is one of the explanations for the disappearance of memory and the decline of other brain functions in the elderly. But, according to a new study from the University of Illinois, there could be a cure for the inevitable: dietary fiber.
Dietary fiber promotes the growth of good bacteria in the intestine. When these bacteria digest the fibers, they produce short-chain fatty acids (SCFA), including butyrate, as by-products.
"Butyrate is interesting because it has been shown to have anti-inflammatory properties on microglia and improves memory in the mouse when it is administered pharmacologically," says Rodney Johnson, professor and department head. animal sciences from the University of Iran. Frontiers in Immunology study.
Although positive results of sodium butyrate – the form of the drug – have been observed in previous studies, the mechanism was not clear. The new study reveals that in old mice, butyrate inhibits the production of harmful chemicals by inflamed microglia. One of these chemicals is interleukin-1β, associated with Alzheimer's disease in humans.
Understanding how sodium butyrate works is a step forward, but researchers were more interested in whether the same effects could be achieved simply by feeding more mice.
"People are not likely to consume sodium butyrate directly, because of its harmful odor," says Johnson. "A convenient way to get high butyrate is to consume a diet high in soluble fiber."
The concept takes advantage of the fact that intestinal bacteria convert fibers into butyrate naturally.
"We know that diet has a major influence on the composition and function of microbes in the intestine and that high-fiber diets are beneficial for good microbes, while diets high in fat and Protein alteration of intestinal microbes is one of the ways in which it affects the disease, "says Jeff Woods, a professor in the Department of Kinesiology and Community Health of the University of Toronto and co-author of l & # 39; study.
Dietary fiber butyrate should have the same benefits in the brain as the drug form, but no one has tested it before. The researchers fed groups of young and old mice with low fiber and high fiber diets, then measured levels of butyrate and other SCFAs in the blood, as well as inflammatory chemicals present in the blood. l & # 39; intestine.
"The high-fiber diet increased butyrate and other SCFAs in the blood, in both young and elderly mice, but only older mice had intestinal inflammation with a low-fiber diet." "It is interesting to note that young adults have not had this inflammatory response on the same diet, which clearly highlights the vulnerability of aging."
In contrast, when older mice consumed a high-fiber diet, their intestinal inflammation was significantly reduced, showing no difference between age groups. Johnson concludes, "Dietary fiber can really manipulate the inflammatory environment in the intestine."
The next step was to examine the signs of inflammation in the brain. The researchers examined approximately 50 unique genes in microglia and found that the high-fiber diet reduced the inflammatory pattern in older animals.
Researchers have not examined the effects of diets on cognition and the precise behavior or mechanisms of the gut-brain axis, but plan to tackle it within the framework of the study. a new grant of nearly $ 2 million from the National Institute. on aging, part of the National Institutes of Health.
Although the study was conducted in mice, Johnson is comfortable extending his findings to humans, if only in a general sense. "What you eat is important – we know that older people consume 40% less fiber than what is recommended, and not eating enough fiber can have a negative impact on brain health and health." 39, inflammation in general. "
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