Your digestive tract is a remarkable machine: it’s a system capable of breaking down the food we eat into building blocks that our body can use for energy, growth and repair. But while that operation is core to our physical health and survival, our digestive system can (and does) do so much more. Let's dig into the gut-brain connection.
What is the Gut-Brain Connection?
Have you ever heard of the term ‘the second brain’? Popularized in 1999 by a doctor named Michael Gershon in his book by the same name, opened the door to explaining the relationship our gut (and the gut flora residing in it) has with our brain.
Why would Dr. Gershon refer to the digestive system as the 'second brain?' The answer lies in the stuff the brain is made of: neurons (aka nerve cells).
How our Nervous System Is Organized
We used to think of the nervous system as having two primary branches.
- The Central Nervous System (CNS) - comprised of the brain and spinal cord
- The Peripheral Nervous System (PNS) - is comprised of everything else (i.e. nerves that control your organs and muscles and allows you to feel sensations like hot and cold)
But do you have a 'gut feeling' that there's something more to this story? You're right: the enteric nervous system.
Gut Feeling: Our Enteric Nervous System
The word "enteric" means relating to (or occurring in) the gut; so in this case we're talking about 'nervous system of the gut.'
What's pretty remarkable about this system (and highlights its importance) is that the enteric nervous system has more neurons than your spinal cord. Unlike other parts of your body, the gut can operate semi-independently, thanks to the power and the autonomy of your enteric nervous system. Your gut quite literally has a mind of its own.
But How Are the Gut and the Brain Connected?
Good question. It's via the vagus nerve, which is basically a giant nerve superhighway that carries nerve transmissions to and from the brain.
Thinking of a highway, picture what it looks like during rush hour. Typically, the flow of traffic is heavier going one way than the other. It's the same with our vagus nerve (minus the traffic headaches). It carries more information from our gut to our brain than it does from our brain to our gut. This is why the term ‘second brain’ makes so much sense. It’s relaying just as much information about the state of our health, mood and well-being as our 'first brain'.
It seems like before we had the science to understand the gut-brain connection, we had a sense that our mood played a role in our digestive system. From ‘butterflies in your stomach’ to having your gut ‘tied in knots’ by stress, to having a 'gut feeling' about something, the English language has many terms alluding to the relationship between our first and second brains.
The Gut-Brain Connection & Mental Health
Research has now started to build out the connections between mental health, gut health and the role of our microbiome, but there are far more questions than answers at this point.
We know that animals raised without an intestinal flora show more anxiety than those with a healthy gut flora. We also know that certain probiotics have shown promise in treating depression and anxiety (although the majority of this research involves animal studies). Stress can even initiate relapses of inflammatory bowel disease and make irritable bowel syndrome worse.
Certain probiotics can influence the level of the neurotransmitters serotonin (our happy hormone) and GABA (a neurotransmitter that promotes relaxation and reduces anxiety).
Locally in the gut, serotonin affects the motility of the gut (i.e. how the gut moves its contents down the line), but there are hints that gut-produced serotonin may have an impact on the brain itself. And medications we take for depression, known as selective serotonin reuptake inhibitors, or SSRIs, can cause gut issues due to serotonin’s multiple functions.
When it comes to GABA, low levels have been associated with depression and anxiety. But studies looking at supplementing mice with Lactobacillus strains, saw consistent changes in GABA-receptors in the brain as well as reduced signs of depression and anxiety. More support for the role our gut flora has in the gut-brain connection.
So now you know your gut, aka your second brain, is critical to your overall health, both physical and mental. When you understand its importance, caring for it should become a part of your daily life. Want to take better care of your second brain? Eat well, exercise, manage stress and consider a clinically proven probiotic!
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The Second Brain. Michael Gershon MD