Today I would like to talk about a seemingly mundane and, let’s face it, slightly disgusting topic. I am talking about the gut.
The gut has a huge autonomous nervous system that is quite similar to our brain. People knew for a long time that the gut has a huge impact on our emotions (although scientists underestimated the gut for quite a while). We have “butterflies in our stomach” when we are in love, we have to “digest bad news” or “have a gut feeling” that something is wrong and we “swallow a comment”. But why would we need a second brain when we already have a very complex brain that works great?
The answer is actually very simple. Our brain is so important and so sensitive that it is protected very well. It is surrounded by a thick layer of bones and meninges and every bit of blood is filtered before it enters the brain. So, the brain is shielded from the rest of the body but still it needs to react quickly to changes in the environment. On the other hand, the gut is exposed to almost everything that is going on: food, hormones, pathogens etc. In fact, the inside of our gut is really the outside of our body. It also has a huge surface and is our biggest sensory organ. So, you can think of the gut as a secret spy that is telling the brain everything that is going on in our bodies. The question is only how they communicate. There is one very important nerve in our body called the vagus nerve. It innervates almost every organ and is responsible for slowing down the heart rate or reducing the blood pressure. Interestingly, 90% of the nerve fibers between the gut and the brain go from the gut to the brain and not the other way around!
The importance of the vagus nerve has been discovered by psychology a while ago. When this nerve is stimulated in different frequencies, test persons feel either anxious or calm. In fact, vagus stimulation is a common tool for the treatment of depressions. Now that we know, that the vagus nerve is important for our emotional wellbeing and we also know that the gut sends signals to the brain via the vagus nerve, might it be possible that the gut is able to influence our emotions?
In fact there is lots of evidence that the gut has an impact on our emotions. As you all probably know, the gut is covered in a huge variety of different bacteria that help us to digest food. In one experiment, researchers added some “good” bacteria (Lactobacillus rhamnosus JB-1) to the food of mice while another group of mice only got their normal food. Then, the mice were put into a water tank and it was measured how long they were swimming. The idea behind that is that depressed mice don’t search for a ground to stand on for a very long time and give up swimming quickly. Those mice that were fed with good bacteria did swim much longer searching for a way out than the control mice. Additionally they had much lower levels of stress hormones in the blood and were better in memory tests. The effects were reversed when the vagus nerve was cut through. This experiment indicates that the gut is able to influence our emotions over the vagus nerve.
Both brain and gut filter, which influences actually get into the brain and which are not relevant enough. This way, not every undigested carrot has an effect on our mood but still we are able to feel cozy and warm after a feast. You can imagine it like a bouncer who won’t let any emotion in. To study the effects of the gut on our emotions, experiments have been done with people who have irritable bowel syndrome. These patients generally have stronger tendency towards depression and anxiety. In one experiment researchers inflated a balloon in the colon these patients and compared their reaction to a healthy control group. Those people with irritable bowel syndrome experienced a feeling of fear and anxiety after the balloon was inflated while the control group was unaffected. If the gut is constantly irritated, like it is in irritable gut syndrome, it leads to increased activities in those brain areas that are usually responsible for negative emotions. These irritations somehow seem to confuse the bouncer that decides which information enter the brain.
On the other hand it was shown that people, who have just consumed lots of fatty acids, show a weaker emotional reaction to sad pictures than people who have eaten saline food. So, when we are searching comfort in food, or even binge eat, it is actually possible to numb our emotions. Don’t get me wrong, I’m not saying that we should numb our emotions by eating. On the contrary, this can lead to a vicious cycle. We feel uncomfortable after we have consumed too much fatty food and will feel unconfident about our bodies on the long term, so we have more negative emotions. Also, overeating fatty food will irritate the bowel and lower threshold for negative emotions that are passed on to the brain even more.
Now we know that the gut actually has a strong but subtle impact on our emotions. What do have to do to keep it happy?
The answer to this question is a little more complicated and requires some background knowledge. So, I will give the answer to this in a second post that is coming soon. In the mean time I would like to know, if you ever experienced a connection between gut and emotions?
All the best!