A Gut Feeling: The Gut-Brain Axis

There’s a reason you feel “butterflies” before your first date and nausea before speaking in front of a crowd–it’s called the gut-brain axis. You see, your gut and your brain are in constant communication with each other. Your brain tells you stomach and intestines what’s its feeling, which I think most people intuitively know, but recently, a lot of research has gone into the opposite relationship. That is, how what’s happening in the gut affects what’s happening in the brain.

As someone who’s dealt with both anxiety and gastrointestinal health issues, the gut-brain axis is particularly interesting to me. I mentioned I’ve read a couple of books on the topic in my “coffee date” post, and I’ve been checking out some of the scientific journal articles as well. Defensive pessimism is one tool that I’ve found to help cope with my anxiety, but I’m always on the look-out for new ideas.

So, with no further ado, onto The Science.

The Gut-Brain Axis

The nervous system and the “gut,” more technically referred to as the  gastrointestinal (GI) tract, communicate with one another through neural pathways (nerves), the immune system, and messengers such as hormones and neurotransmitters. A more recently discovered “spokesperson” for the gut is its microbiota. The microbiota is the community of bacteria (a.k.a. microbes) that live in the gut. An alteration in the composition of the gut microbiota is called dysbiosis.

If your gut and your brain were to post a relationship status on Facebook, it would be “It’s complicated.” The brain influences the gut. But the gut also influences the brain. And both influence each other through a variety of methods and mechanisms.


If you have inflammatory bowel disease, irritable bowel syndrome (IBS), or coeliac disease, then you may have a dysbiosis in your own gut. GI disorders have also been associated with anxiety disorders and depression.

Taken together, these associations have led scientists to suggest that gut bacteria play an important role in mood and behavior. So it would seem that your bacteria is pretty important to you as an individual. But where do your microbial companions even come from?

The Mouths (and Guts) of Babes

For all intents and purposes, the human intestinal tract is sterile at birth. That doesn’t last long though. When delivered naturally, vaginal bacteria immediately takes up residence in the wailing baby. After C-sections, bacteria from the mother’s skin soon inhabit the tiny, shriveled human. During a baby’s early life, the gut microbiota develops rapidly, until an adult-like community arises.

Mammals and bacteria have co-evolved to live together in mutual harmony and benefit. The bacteria help their mammalian hosts to convert non-digestible fiber to accessible short-chain fatty acids, defend against other dangerous bacteria, and modulate the immune system. For its part, the host’s gut provides a nutrient-rich home for its bacterial companions.

Studies performed with animals have proved the importance of microbiota in the proper maintenance of the body’s functions. In particular, mice raised “germ-free”–completely sterile–have physiological and metabolic abnormalities. (Scientists LOVE mice, so a lot of microbiome-gut-brain axis research out there is based on mouse studies.)

Stress and Digest

Being stressed increases susceptibility to GI disorders. Stress also alters gut microbiota. Scientists have suggested that gut microbiota and stress feed into each other in a “self-perpetuating” loop.

If stress alters the type, variety, and number of bacteria in our guts, then stress can also open use up to invasion by pathogenic (“bad”) bacteria. Just in case you didn’t have enough reasons to try to get your stress under control.

But what about the other direction of the loop? What can we do to improve the health of our guts and maybe, just maybe, the health of our brains?

You are What you Eat

This is where the science gets a lot fuzzier. While the gut-brain axis is well-recognized and lots of associations between the microbes in the intestines and the activity of the brain have been found, definitive conclusions and recommendations are a little trickier.

You’ve probably heard a lot about probiotics–the hipper counterpart to antibiotics. WebMD says this on the subject:

Probiotics are live bacteria and yeasts that are good for your health, especially your digestive system…..Probiotics are naturally found in your body. You can also find them in some food and supplements.”

There’s currently a huge market in supplemental probiotics, but it’s important to note that although some probiotics have shown promise, robust scientific does not yet exist to support probiotics as a treatment for most health conditions. The U.S. FDA has not approved any probiotics for prevention or treatment of any health condition, and the NIH points out that the marketing and use of probiotics have gone beyond the actual scientific research on the subject.


So, after examining some of the science related to the topic and recognizing that I have barely brushed the tip of the gut-brain iceberg, I’m still working on formulating my own opinions and plans on how to proceed. I’m not planning to go out and buy hundreds of dollars worth of probiotics or start playing Mozart for my microbes in order to make them happier and smarter. I am, however, working on incorporating more probiotics into my diet through foods. I already eat yogurt (of the plain and Greek variety) for breakfast nearly every day, but other than that, I have some work to do. My interest in probiotics is more related to their possible GI benefits than to any anxiety/mood benefits for now, as I feel that the latter still needs more research.

Aside from that, I am working on getting over the sticker-shock and buying more meat, eggs, and dairy that come from animals not treated with unnecessary antibiotics and hormones.

And I am continuing to read up on the subject, because why would I want to do any of the reading my professors assign me when I could spend hours scouring the internet for information about gut flora?

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