The new research was published in the journal Microbiome. It was the work of researchers associated with a university in China and another in Australia.
The researchers noted that age-related cognitive decline is observed in the developed world. Low fiber intake is also a common feature of diets in these countries. The study notes that the average fiber intake in the US and UK is around 15g / day, well below the World Health Organization recommended level of 25-35g / day. . The average fiber intake in China is even lower at 11g / day, they said.
The objective of the present study was to find whether there is a mechanistic relationship between the two via the gut-brain axis.
To test this hypothesis, the researchers obtained 60 mice evenly divided between the experimental and control groups. The control group ate food with about 20% by weight of dietary fiber from various plant sources such as corn, soybeans, wheat, oats, alfalfa, and beets. The other group had a diet low in fiber but high in sucrose and simple starch.
The changes in the gut began to appear quickly
To test how quickly the intestinal changes took place, half of the mice in each group were euthanized after seven days.
Long-term mice ate their respective diets for 15 weeks and were subjected to a series of tests including how well they organized a nest when provided with nesting material, how well they remembered location of objects and other measurements.
The researchers analyzed stool samples from all four groups and observed marked differences between the groups. In low fiber groups, the BacteroidetesPhylum has shrunk and organisms in the Proteobacteriaphylum increased.
The low-fiber group also had a thinning of the intestinal mucous layer, as revealed by the alcian blue staining. A thinned mucous layer is associated with greater intestinal permeability, which can lead to higher levels of serum lipopolysaccharide which in turn are associated with neuroinflammation.
The low fiber group performed poorly on cognitive and “daily activity” tests
The bacterial and mucosal changes were seen early in the study, even before the effects of cognitive impairment began to appear, the researchers said.
Fiber-deficient mice performed poorly on the nest-building test (a “daily activity”) and could not remember the location or order of objects as well as their more fiber-rich peers. The low-fiber group also showed degenerative changes in a particular region of the hippocampus, as shown by transmission electron microscopy. And some proteins indicating neuroinflammation were higher in the low-fiber group.
Define the role of the SCFA
The researchers also noted that the levels of butyrate, acetate and propionate, the three short-chain fatty acids associated with bacterial fermentation of dietary fiber in the gut, were lower in the fiber-deficient group. The researchers decided to do a side-by-side experiment to test whether the shortage of these SCFAs was part of the mechanism of cognitive decline, as has been suggested by other studies.
They supplemented another low-fiber group with all three SCFAs for an additional 15 weeks. Mice that were so treated – a low-fiber diet but with additional SCFAs – performed better on object tests and nest-building exercise than their low-fiber peers and also showed markers. weaker neuroinflammation and slightly thicker intestinal mucous layers.
“This study, for the first time, reports that a low-fiber diet leads to cognitive impairment by altering the gut microbiota-hippocampus axis, which is pathologically distinct from normal brain aging. These findings alert to the negative impact of dietary fiber deficiency on brain function and highlight increased fiber intake as a nutritional strategy to reduce the risk of developing cognitive decline and associated neurodegenerative diseases. to food “,the authors conclude.
9, Item number: 223 (2021)
A low-fiber diet causes cognitive impairment and synaptic loss mediated by hippocampal microglia through the gut microbiota and metabolites
Authors: Hongli Shi, Xing Ge, Shi Ma et al.