The researches confirm what we see in clinic:

‘Our results are indisputable: certain bacterial products of the intestinal microbiota are correlated with the quantity of amyloid plaques in the brain’, – explains Moira Marizzoni.

‘Alzheimer’s disease is the most common cause of dementia. Still incurable, it directly affects nearly one million people in Europe, and indirectly millions of family members as well as society as a whole. In recent years, the scientific community has suspected that the gut microbiota plays a role in the development of the disease.

‘A team from the University of Geneva (UNIGE) and the University Hospitals of Geneva (HUG) in Switzerland, together with Italian colleagues from the National Research and Care Center for Alzheimer’s and Psychiatric Diseases Fatebenefratelli in Brescia, University of Naples and the IRCCS SDN Research Center in Naples, confirm the correlation, in humans, between an imbalance in the gut microbiota and the development of amyloid plaques in the brain, which are at the origin of the neurodegenerative disorders characteristic of Alzheimer’s disease.’

‘Indeed, high blood levels of lipopolysaccharides and certain short-chain fatty acids (acetate and valerate) were associated with both large amyloid deposits in the brain. Conversely, high levels of another short-chain fatty acid, butyrate, were associated with less amyloid pathology.’

https://medicalxpress.com/news/2020-11-link-alzheimer-disease-gut-microbiota.html