Prebiotics: What We Currently Know About Their Use in Neuropsychiatric and Neurodegenerative Diseases

One of the questions I get asked the most by my readers is “what prebiotic and/or probiotic is the best?”  Unfortunately, there is no good answer to that because we just don’t have the research to know.  To boot, everyone’s body is different.  Still, to help you all out as best as I can, I just finished reading a year-old paper on what we know about using prebiotics to treat anxiety, depression and cognitive issues.[i]  You’ll never believe it (ha!) but there are not even vaguely enough clinical trials to know how to optimize their use.  That said, there are some really interesting highlights in the paper and we can certainly conclude that prebiotics do play a potential role in helping alleviate symptoms.

The paper starts with emphasizing the fact that the main factor in determining the quality and quantity of microbiota is diet.  And we know that the microbiota is a fundamental regulator of both intestinal and brain health, and the immune system.  We also know that inflammation is one of the critical processes underlying several neurodegenerative and neuropsychiatric disorders including major depressive disorder (MDD), Alzheimer’s Disease (AD), Parkinson’s Disease (PD) and many others.  Thus, the authors state, “…nutritional elements such as probiotics and prebiotics, could improve the host health due to their immunoregulatory properties.”

Probiotics and prebiotics that influence the brain are called psychobiotics.  I first wrote about that new term way back in 2016 – see here.  These can have anxiolytic (anti-anxiety) and anti-depressive effects, as well as altering cognition and emotions.  This particular article reviewed what we currently have in terms of research on the effects of prebiotics, which, the authors state, “…may be useful as a potential therapeutic tool for cognitive impairment, anxiety and depression.”

A quick review:  prebiotics refer to both digestible and non-digestible fibers that feed the microbiota.  Many foods are rich sources including onions, garlic, bananas, asparagus, and more.  Simply through eating a wide variety of fruits and vegetables, you are consuming a nice array of different prebiotics.  We know that by promoting the growth of beneficial bacteria, prebiotics help with the maintenance of the intestinal barrier and reduce circulating levels of inflammatory markers (including IL-6, TNF and c-reactive protein).  They can directly prevent the invasion of pathogens by “…decreasing endothelial adhesion due to their anti-adhesive property.”  I thought that was particularly interesting in light of that research I posted earlier this week, on a fungus that adheres to the inflamed and damaged tissue seen in Crohn’s disease, preventing wound healing.  Finally, prebiotics promote the grown of bacteria that produce stress neuromodulators as well as short-chain fatty acids, about which you have read a lot on this blog.  So, all in all, the right prebiotics have tremendous beneficial potential.

There are too many studies reviewed in the paper for me to go into them all so I’ll just give you a small sampling:

1. “Several studies with prebiotics and AD have shown beneficial effects on cognition.” Chitosan oligosaccharides (COS) are anti-inflammatory, antioxidants, immune regulators and also have neuroprotective effect.  Studies have shown that they attenuate some symptoms of AD in animal models.
2. Fructooligosaccharide (FOS), again in animal models, has shown positive neural effects, increasing levels of affected neurotransmitters (acetylcholine, serotonin, etc.) and decreasing damage to parts of the affected hippocampus. 6 weeks of administration in animals showed measurable cognitive improvements in the animals.  In a mouse model, it reduced neurodegeneration.
3. Inulin, which is structurally similar to FOS, “…exhibits impressive results in cognition.” In humans, it has been shown to lead to “…greater accuracy in memory recognition and recall tests.”
4. A recent clinical review of prebiotics showed that doses of 5-10 grams per day are safe and improve learning and memory and behavior. However, this was tested in young to middle aged people who are healthy.
5. Prebiotics show some promise in MDD. FOS combined with GOS (galactooloigosaccharides) appear to possess antidepressant- and anxiolytic-like effects in rodents.
6. Baker’s yeast beta-glucan, given for 12 weeks, reduced both upper respiratory infections as well as improved mood in stressed women, who are more susceptible to colds and other upper respiratory illnesses.
7. Two capsules per day of the symbiotic (combination of probiotic and prebiotic), Familact H, was tested in a small double-blind and placebo-controlled trial, and showed efficacy in the treatment of moderate depression.
8. 44 patients with irritable bowel syndrome (IBS), who also had anxiety issues, were given BGOS (bumono-galacto-oligosaccharides). This prebiotic is selective for Bifidobacterium, which improves lower gut health.  After being given either 3.5 or 7 grams of the prebiotic for 3 months, the patients showed, “…a significant increase in fecal Bifidobacteria and improvement in IBS symptoms, such as flatulence and swelling.”  They also all showed improvements on anxiety scores.
9. Studies done on anxiety show that “…prebiotic administration leads to the amelioration or prevention of depression and anxiety.
10. The authors conclude that “…prebiotics appear to be relevant candidates for the adjunctive treatment of anxiety and depression and cognitive dysfunction in neurodegenerative and neuropsychiatric diseases. Besides, these compounds can ensure healthy aging, retarding memory and learning loss in the elderly.”

Unfortunately, clinical studies are “scarce.”  Most, as you can see, are done on animals because of the overwhelming expense of human trials.  Still, I hope this post gives at least some guidance and/or ideas to those of you who would like to add prebiotics to your daily regime.

 

[i] Paiva IHR, Duarte-Silva E, Peixoto CA. The role of prebiotics in cognition, anxiety, and depression. Eur Neuropsychopharmacol. 2020 May;34:1-18. doi: 10.1016/j.euroneuro.2020.03.006. Epub 2020 Mar 30. PMID: 32241688.