If you’ve ever had a “gut feeling”, made a decision and “gone with your gut”, or “had butterflies” before something nerve-wracking, you’re likely receiving signals from an unlikely source — your digestive system.
Your gastrointestinal (GI) tract is lined with two thin layers of more than 100 million neurons from your oesophagus to your rectum. This is called the enteric nervous system (ENS) and scientists refer to this as your “second” brain, your “little” brain, or your “brain in your gut”.
It has long been thought that depression and anxiety contributed to these digestive conditions; however, it appears that it is in fact the other way around.
The gut is also connected to our emotional limbic system, which is responsible for mood. This is why, when someone is experiencing irritable bowel syndrome (IBS) or functional bowel problems, they may also experience depression and anxiety.
It has long been thought that depression and anxiety contributed to these digestive conditions; however, it appears that it is in fact the other way around — irritation in the GI tract may send signals to the brain that trigger changes in mood.
The Brain in Your Gut
If you were to stretch the gut out, it would stretch 40m — the length of a tennis court. And if you were to unroll it and flatten it out, it would cover 400m2. The brain in the gut is autonomous, it is the size of a cats brain, is organised into autonomous microcircuits (it senses food and knows exactly what to do), senses food by chemical and mechanical means, mixes all the various elements which we need for digestion, controls the specific contraction of muscles (it also has a reflex to push food back out), and controls the secretion of molecular machinery which digests food.
While the gut is autonomous, it is closely linked to the higher brain. These two organs are connected both physically and biochemically. They are connected physically by the vagus nerve and biochemically through neurotransmitters.
The vagus nerve is the longest and most complex of the twelve pairs of nerves that emanate from the brain. Most interestingly, it sends signals in both directions, meaning that the gut and brain are highly influenced by each other.
Neurotransmitters are chemical messengers that control feelings and emotions. Serotonin is a well-known feel-good chemical produced in the higher brain. But a large portion of it is also produced in your gut by your gut cells and the trillions of microbes living there.
The trillions of microbes that live in your gut also produce chemicals that affect how your higher brain works. Microbes can be bacteria, viruses, fungi and other microscopic things. There are approximately 40 trillion bacterial cells in your body — we only have about 30 trillion human cells, meaning you are more bacteria than human.
By altering your gut microbes, you also alter your higher brain. Your gut microbes are altered by everything you put into your mouth. The types of foods specifically beneficial for your gut microbes, and therefore your gut-brain connection, and hence your higher brain, are omega-3 fats (oily fish), fermented foods (yoghurt, kefir and sauerkraut), fibre (grains, nuts, seeds, fruits and vegetables), polyphenol-rich foods (cocoa, green tea and olive oil) and tryptophan-rich foods (turkey, eggs and cheese).
Your GI tract is lined with so many nerve cells that scientists refer to it as your “second” brain. The two-way connection between the higher brain and the “lower” brain through the vagus nerve, both physically and biochemically, means that each directly affects the other. By consuming a diet that supports the trillions of microbes in your gut, you also support your brain, and this directly influences your mental health.
Have you ever experienced a change in your feelings and emotions from the food that you eat?
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