The gut talks back

February 4, 2019

There is a highway for communication between the gut and the brain that allows messages to be sent in both directions.  It’s called the gut-brain axis.  A frequent sender of messages along the highway is the community of microbes in the gut.  They play a critical role in gut health, but they also play a role in the development and function of the brain.

Mounting evidence indicates that the microbes in the gut affect a person’s mood.  One study showed that certain types of bacteria like Bacteroidetes, Proteobacteria, and Actinobacteria tend to be in high abundance in the intestines of people who are acutely depressed.  In those same people, the levels of a bacterium known as Firmicutes are lower.  In another study, scientists were able to transfer anxiety from one group of mice to another through fecal microbiota transplantation.

While we are learning a lot about how the microbes in the gut impact human health in multiple ways, we do not yet have a good understanding of what a “healthy” microbiome looks like.  If we could engineer the perfect microbiome for optimal health, which bacteria would be included, what would their ratios be, and which bacteria would be excluded?  Many research groups are working on the answers to these questions, but it is complex because it isn’t simply about the bacteria themselves.  The microbiome is influenced by factors like diet, genetics, and the environment.

The good news is we don’t have to wait to learn everything before we can start using the information scientists have discovered so far.  We know that certain bacterial strains are beneficial for us.  Those are called probiotics.  We also know that probiotics thrive when we feed them prebiotics.  While the understanding of the science behind this is relatively new, it’s been known for centuries that fermented foods, natural probiotics, are good for maintaining gut health.

The bad news is that there is a danger to acting on partial information.  There is still a lot that we don’t know about the gut microbiome and the gut-brain axis.  It is easy to listen to the advertisements of the nearly $100 billion probiotic market and load up on probiotic pills and probiotic water and yogurt with extra probiotic strains, but we are still learning how that will impact your health.  There is such a thing as too much of a good thing.

What we need is more clinical evidence on how the gut microbiome affects the brain and leads to or prevents feelings like stress, depression, and anxiety.  We need that evidence to cover a broad range of probiotic strains and for multiple studies to examine the effects of the same probiotics.

In addition to knowing what happens when we add more probiotics to our diet, we need to know what happens to the makeup of the gut microbiome when we take antibiotics.  Not every antibiotic works the same way, so we need that information for each new antibiotic.

We also need an understanding of the effects of fecal microbiota transplants.  Clinical evidence supports fecal microbiota transplants for some patients, but in general, there is still a lot that we don’t understand about how the transplanted microbes will affect the patient, as was seen in the experiment where anxiety was transfer through transplanted microbes.

Whenever making changes to your diet or lifestyle, it is important to be informed.  The science is strong behind some of the latest trends in health but weak behind others.  Staying informed is the only way to make the best choices you can for your health given the information that is available.  To stay up-to-date on the latest in gut health, follow the ETP blog.  If there’s a topic you are interested in learning more about, please email us at

If you’re interested in the scientific details, check out the following scholarly reviews.

Dinan TG, Cryan JF. Mood by microbe: towards clinical translation. Genome Med. 2016 Apr 6;8(1):36.

Dinan TG, Cryan JF. Gut-brain axis in 2016: Brain-gut-microbiota axis – mood, metabolism and behaviour. Nat Rev Gastroenterol Hepatol. 2017 Feb;14(2):69-70.

MacQueen G, Surette M, Moayyedi P. The gut microbiota and psychiatric illness. J Psychiatry Neurosci. 2017 Mar;42(2):75-77.

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