As mammals get older, immune cells in the brain, called microglia, become chronically inflamed.
“Microglia cells account for about 10% of all glial cells in the central nervous system (CNS). Classically, microglia cells are considered to be the first immune defense barrier of the CNS, activating very rapidly in response to inflammation.
Nevertheless, in a physiological situation, the microglial cells also appear very dynamic, constantly projecting dendrites that palpate and monitor their micro-environment.
Some dendrites interact directly with the synapses of neighboring neurons. This contact activity could be involved in the control of synaptic connections. “
In this state of inflammation, microglia cells 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.
According to a study from the University of Illinois (USA) published Aug. 14, 2018 in the journal Frontiers in Immunology , there could be a cure for the inevitable: dietary fiber . Remember that the main sources of fibercome from vegetables and fruits , grain products , legumes and nuts .
DIETARY FIBER REDUCES BRAIN INFLAMMATION DUE TO AGING
Dietary fiber promotes the growth of good bacteria in the gut. When these bacteria digest the fibers, they produce short-chain fatty acids (SCFA), including butyrate (which is a salt or butanoic acid ester), 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 administered pharmacologically.
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Although positive results of sodium butyrate (the form of the drug) have been observed in previous studies, the mechanism was unclear.
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This new study reveals that in old mice, butyrate inhibits the production of harmful chemicals by inflamed microglia. One of these chemicals is interleukin-1, which is 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.
The researchers point out that “people are not likely to consume sodium butyrate directly, because of its harmful odor, but 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.
Diet has a major influence on the composition and function of microbes in the gut. Diets high in fiber are beneficial for good microbes. Dietary fiber butyrate should have the same benefits in the brain as the drug form, but no one has tested it before.
A DIET RICH IN FIBER REDUCES THE INFLAMMATORY PROFILE
For this study, the researchers fed young and old groups of mice with diets low in fiber and high in fiber, and then measured the levels of butyrate and other SCFA in the blood, as well as inflammatory chemicals present in the intestine.
The high-fiber diet increased butyrate and other SCFAs in the blood, both in young mice and aged mice. But only older mice had intestinal inflammation with a low fiber diet.
It is interesting to note that young adults did not have this inflammatory response on the same diet. This 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. The authors state that “dietary fiber can really manipulate the inflammatory environment in the gut. “
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 address them in a future study.
Finally, although the study was conducted in mice, researchers are very confident about extending their findings to humans, if only in a general sense.
To conclude, the researchers point out that “what we eat is important” and “the elderly consume 40% less dietary fiber than is recommended. Failure to consume enough fiber could have negative consequences on cerebral health and inflammation in general. “
Cereals rich in soluble fiber.
WHAT ARE THE RECOMMENDED DAILY INTAKES OF DIETARY FIBER?
The recommended daily intakes of dietary fiber allow to have a good intestinal transit. The intakes for an adult are about 25 to 45 grams of fiber a day.
It is advised for the men of 19 – 50 years: 38 g; for women aged 19-50: 25 g; for men 50 years and older: 30 g; for women aged 50 and over 21 g.
WHICH FOODS ARE HIGH IN DIETARY FIBER?
Soluble dietary fiber comes mostly from cereals, mainly unrefined cereal products.
The best sources of dietary fiber are legumes, dried fruits, whole grain products, and some vegetables and fruits.
Lists of high fiber foods : cinnamon, wheat bran, oat bran, whole grains, wheat cereal, coconut, almonds, black olives, dried figs, dried prunes, blackcurrant, dried beans, dark chocolate, vegetables , psyllium.