Feeling nervy? Microbiota-gut-brain connections
As we dug intoon December 1st, microbiome has been the IT word for 2018.
We found out a bit about why the microbiome is so fascinating, and we saw a lot of ways that our guts and brains affect each other. But, how can this be?
How is it that these microbiota-gut-brain connections actually work?
I was wondering the same thing, and for a long time all I found were references to the Vagal Nerve. Turns out, the microbiome-gut-brain axis is a complex one. It involves connections between nerves, yes, and also biochemicals, and the immune system itself.
And that’s what we know now – and what I’ve been able to find and understand. This is a hotbed of research and more details are sure to surface in the near future.
Let’s look at each one of these separately.
The microbiome-gut-brain axis: The nerve connections
In terms of nerves themselves, there are a few ways the microbiome and gut connect with the brain.
First, your gut has a lot of nerves and is sometimes called the “second brain.” All these 200-600 million nerve cells together form their own nervous system called the “enteric nervous system.” These nerve cells control the intricate functions necessary for your digestive system to do its job – from release of digestive enzymes, to movement of food through it, to the blood flow around it that picks up the absorbed nutrients. The gut uses its own brain to function optimally.
This enteric nervous system is so important, but unbelievably, did not even factor into the considerations of most metabolic scientists or doctors, as recently as 1990s!
The second nerve connection between your gut and your brain is through the vagus nerve. This is the one nerve I mentioned before – it is a huge one that physically connects our gut with our brain.
The vagus nerve has been shown to send about 80% of the info from your gut up to your brain – and not from your brain down to your gut as we previously thought!
The vagus nerve is part of the nervous system that controls the body subconsciously, called the “autonomic” nervous system (it works “automatically”).
This system is divided into two parts: sympathetic and parasympathetic. The sympathetic part controls our “fight or flight” stress reactions. The parasympathetic part, containing the vagus nerve, controls our “rest and digest” functions.
Which makes sense, considering it links the digestive system to the brain.
The information travelling to the brain through the vagus nerve is from the gut as well as its microbiota.
The second way the microbiome and gut link to the brain is through biochemical connections.
In addition to the physical nerves that surround our gut (enteric nervous system) and the nerve that carries info from our gut and microbiota to our brain (vagus nerve), there are biochemical connections.
The first type of biochemical that sends information from our gut to our brain are neurotransmitters.
“Neurotransmitters” are just that – transmitters of information between nerve cells. They’re chemical messengers that allow nerve cells to communicate with each other. One of the most famous mood-affecting neurotransmitters, serotonin, is made in the gut. Serotonin is sometimes called the “happy” neurotransmitter because it seems to be lower in people with depression.
Research shows that 90% of serotonin is in the gut, not in the brain! It plays an essential role, promoting the movement of food through the gut (peristalsis).
Another biochemical connection is between our gut microbes and our brains – through their metabolites.
Our gut microbes need to eat, and in the process they produce compounds (i.e. metabolites). These include short chain fatty acids from dietary fibre, as well as amino acids from dietary protein. As mentioned earlier, they also create the essential vitamins B12 and K. All of these microbial compounds travel throughout our bodies and can reach and affect our brains.
The third biochemical connection between our microbiome, gut, and brain – is through stress hormones.
Our HPA-Axis (Hypothalamic-Pituitary-Adrenal Axis) starts in our brains and uses hormones like cortisol to affect other parts of the body, including the gut. Research shows that stress hormones tell immune cells in the gut to secrete compounds that can cause inflammation and tiny “leaks” in the gut (permeability).
In addition to the physical nerve connections and the biochemical ones the microbiome-gut-brain axis also uses the immune system.
The microbiome-gut-brain axis: The immune and inflammatory connections
Our immune cells travel throughout our body looking for unwelcome invaders like harmful bacteria and viruses. Just like most of our neurotransmitter serotonin is located in our gut, most of our immune system is there too!
This is because our mouths are a huge portal for the outside world to get into our bodies. We can easily swallow disease-causing microbes which need to be dealt with by our immune system. So, it makes a lot of sense that most of our immune system is located around our gut.
When our immune cells start working to attack invaders, they can cause inflammation.
If our immune cells become overactive, this can cause Auto-Immunity and excess inflammation.
DID YOU KNOW? This connection is why most autoimmune conditions have a name that ends with -itis (like Hashimoto’s thyroiditis) – they’re related to inflammation, and inflammatory conditions (like conjuntivitis, arthritis) get the -itis suffix.
Autoimmunity is when our immune cells mistake our own cells as harmful ones, and then attack them. This can also affect our moods!
All 3 connections, the nervous, the biochemical, and immune, compose the complex microbiome-gut-brain axis!
There is a clear 2-way street between our gut and our brains, even though the details are still being discovered as we speak.
These discoveries have greatly impacted my work as a nutritionist. From what we know already, we have been able to understand to a much better degree why certain foods affect our health the way they do!
Let’s talk about how what we eat affects us next.
In my next post, I’m going to outline what we can put in our gut to feed our moods, and what we can do mentally to help our gut.
Tune in for that part, it is something you can DO to share your health for the better!!