The following, and more, is available at my blog article Microbiome and Probiotics: Gut bacteria can affect your mental health?
Answer to Question 1:
Can poor mental health affect the bidirectional communication between gut microbes and the brain?
Even though there is cross talk between your enteric nervous system (ENS) and your brain, researchers assumed that microbes did not play into it. But recent breakthroughs are challenging that assumption, and changing our understanding of how the blood brain barrier works, because the microbiome can affect your brain in some pretty big ways.
The ENS is a massive web spread over your entire digestive tract made up of more than 500 million neurons that control your guts. This second brain as it is sometimes called, is pretty much self sufficient, and can take care of most of its jobs by itself. But it is connected to the CNS through your vagus nerve, which is an information superhighway between your gut and your brain.
Stress affects your microbiome
Early research starting in the 1970s (Tannock & Savage, 1974) showed that stress could affect the kind of microbes found in the guts of mice. One group found that stressing mice by depriving them of food or water, caused them to have more coliform bacteria like E.coli, and less of another form of bacteria called lactobacilli in their intestines.
Another group found that the stress of dealing with an aggressive cage mate led to changes in amounts of other kinds of bacteria. They found increased numbers of Bacteriodes and Clostridium, along with decreased numbers of Coprococcus, Pseudobutyrivibrio and Dorea.
But even though it was clear that stress could affect the kinds of microbes in the intestines, it wasn’t clear if that was a 2 way relationship.
Could Gut microbes be affecting psychological stress levels?
The first big break on this question came when some scientists from Kyushu University, Japan (Sudo, et al. 2004), discovered that exposure to certain kinds of microbes had dramatic effects on brain chemical levels.
For this study, the scientists used germ free mice. These were mice delivered by C section and immediately put into super clean cages, so they were barely exposed to microbes at all. They also made comparisons with specific pathogen free mice. These were mice only exposed to a known set of microbes.
The germ free mice got a lot more stressed when they were restrained, so it was something about the bacteria in the specific pathogen free mice that was helping them with their stress levels.
The team found that the germ free mice had less of a protein called Brain-derived neurotrophic factor (BDNF). BDNF is important for learning, memory, and higher order thinking. The germ free mice had less of it in the brain regions that determine how an animal reacts to stress.
Answer to Question 2 and 3:
Can consuming products containing probiotics be used to help with mental health problems? If so, can consuming products containing probiotics when well cause mental health problems?
There is not a lot of research that is very clear on the relationship between the gut and the brain in humans. These discoveries are so new that nobody has been able to do any large scale studies in humans yet. But along with prebiotics (fibre suppliments designed to feed good bacteria), small studies have tried treating volunteers with probiotics, deliberately introducing new microbes in to there guts, and the microbes and fibre affected the subjects mood and cognition.
So there might be a relationship between your microbiome and your mental health. But the studies have not been able to look closely enough at what exactly the prebiotics and probiotics are doing to the microbes in the gut, or how that may be translating in to changes in mood.
What does this mean?
Researchers will be getting more into the nitty gritty of these relationships and trying to work out whether these discoveries can translate into medical treatments.
Other scientists are trying to work out how to humanize the mouse microbiome, making the mouse microbiome more human like. They are doing this by taking faecal matter from sick and healthy human patients and inserting them into mice to study the effects.
That kind of experiment can let researcher pick apart how differences in the microbiomes connects with changes in mental health. They can also get right into the brains of mice in ways they can’t with human patients, using dissected tissues to look directly at the structures of brain cells and how they connect.
Can we tailor our microbiome for maximum benefit?
Some researchers are also trying to figure out how specific kinds of microbes are affecting our brains and how we can tailor our microbiomes to maximize the health benefits.
Others are starting to ask questions about how other things that affect our microbiomes like antibiotics could be affecting our mental health and cognition.
So there is still a lot we don’t know about how our microbiome can affect our brain. But there are a lot of new studies in the works and scientists and doctors are hoping that as our knowledge of how our Brain-Gut-Microbiome Axis grows, so will our ability to tweak it and hopefully improve some lives along the way.
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