Don't miss out on exclusive discounts, news, articles and promotions that all our newsletter subscribers get to enjoy every month. If you sign up now, you also get a 10% discount on your first purchase!
We live in a microbiotic world where we are constantly surrounded by bacteria, viruses and fungi - also called microbes. In our bodies there are several billion microbes and 99% of the human body's genetic code belongs to these microbes , where the intestines form the largest microbial community. For hundreds of thousands of years, we humans have developed a very important cooperation with these organisms. If this cooperation does not work or our microbes in the intestines are out of balance, it has consequences for our entire health.
Scientists have long been able to see a connection between an upset stomach and conditions affecting the brain - the microbes in the intestines have an effect on the brain. The stomach and the brain have a direct connection between each other. The two are far apart in the body and have different main functions. However, the state of the gut, and specifically the microbes that live in our guts, the microbiota, actually affects our brain.
The gut-brain axis is a collective name for the communication pathways between the intestines (where about 2 kg of microbes live) and the brain. Communication takes place, among other things, via the nervous system, the blood and the immune system.
As I said, the gut-brain axis represents the gut and brain's different ways of communicating, some ways of communication are more direct than others. The vagus nerve, which is one of 10 nerves whose root is in the brain, is the fastest and most direct link between the gut and the brain. The threads of the vagus nerve extend into the intestinal wall, where they are, among other things, reached by molecules from the microbes. These molecules, eg serotonin, dopamine, glutamate and GABA, can affect signals that travel to the brain through the vagus nerve fibers and thus have an effect on the nerve cells in the brain.
The gut-brain axis also has indirect communication, which mostly happens via the microbes' waste products. Like us humans, many of the microbes in our gut have a metabolism. There, different microbes produce different kinds of small molecules from the broken down food in our gut. These small molecules can both be transported through and communicate with the cells of the intestinal wall, allowing these molecules to reach or initiate reactions that affect the body. A rather well-studied waste product from the bacteria in our gut is short fatty acids, Short-Chain Fatty Acids (SCFAs), whose primary source is bacteria that break down fiber in the gut (fiber from the food or dietary supplements with prebiotics/fiber that we eat) . These fatty acids can be transported through the intestinal wall and are found in small amounts in the blood and spinal fluid. SCFAs affect many processes such as the ability of the intestinal wall to keep tight, stimulation of the vagus nerve and immune system processes.
The neuroendocrine system is the interaction between hormones and the nervous system, where the HPA axis* is the part of the neuroendocrine system that is responsible for the body's stress signals after psychological and physical stressors. The microbiota and the HPA axis appear to have a two-way communication, where e.g. an activated HPA axis, i.e. increased stress, seems to be able to lead to an increased permeability in the intestinal wall (leaky gut) and a microbe-driven inflammation.
* The HPA axis is activated when we become stressed and then the hypothalamus, pituitary gland and adrenal glands work together (HPA stands for hypothalamus-pituitary-adrenal gland in English). So by measuring cortisol it is possible to measure the body's response to stress.
As we mentioned initially, the human microbiome is composed of communities of bacteria, viruses and fungi that have a greater complexity than the human genome itself.
We've also talked about the communication system between your gut and brain called the gut-brain axis. They are linked both physically and biochemically in a number of different ways. They can even affect each other's health.
These sensations coming from your gut indicate that your brain and gut are connected. Additionally, recent studies show that your brain affects your gut health and your gut may even affect your brain health.
The gut-brain axis is a term for the communication network that connects your gut and your brain. These two organs are connected both physically and biochemically in a number of different ways.
Neurons (neurons are cells found in your brain and central nervous system) tell your body how to behave. There are approximately 100 billion neurons in the human brain. Interestingly, your gut contains 500 million neurons, which are connected to your brain through nerves in your nervous system. The vagus nerve is one of the largest nerves connecting your gut and brain. It sends signals in both directions.
In an animal study, it was seen that stress inhibits the signals sent through the vagus nerve and also caused gastrointestinal problems. Similarly, a human study found that people with irritable bowel syndrome (IBS) or Crohn's disease had decreased vagal tone, indicating impaired function of the vagus nerve.
An interesting study on mice found that if you gave them probiotics, the amount of stress hormones in the blood decreased. But when their vagus nerve was cut, the probiotics had no effect. This suggests that the vagus nerve is important for the gut-brain axis and its role in stress.
Your gut and brain are also connected through substances called neurotransmitters. Neurotransmitters produced in the brain control our emotions.
For example, the neurotransmitter serotonin contributes to feelings of happiness and also helps control your body clock. Interestingly, many of these neurotransmitters are also produced by your gut cells and the trillions of microbes that live there. A large part of serotonin is produced in the intestine, for example.
Your gut microbes also produce a neurotransmitter called gamma-aminobutyric acid (GABA), which helps control emotions like fear and anxiety. Studies on laboratory mice have shown that certain probiotics can increase the production of GABA and thereby reduce anxiety and depression-like behavior. GABA also promotes sleep and strengthens sleep quality.
The trillions of microbes that live in your gut also make other substances that affect how your brain works. Your gut microbes produce lots of short-chain fatty acids (SCFAs) like butyrate, propionate, and acetate. They make these short chain fatty acids by using fiber from the food/supplements you eat. SCFAs affect brain function in a number of different ways, and one example is decreased appetite.
One study found that taking propionate can reduce food intake and reduce brain activity related to reward from high-energy foods.
Another SCFA, butyrate, and the microbes that produce this fatty acid are also important in forming the barrier between the brain and the blood, called the blood-brain barrier. The blood-brain barrier constitutes an important and selective mechanical barrier that prevents unwanted molecules and cells found in the bloodstream from entering the cavity where the brain is located.
Gut microbes also metabolize bile acids and amino acids to produce other substances that affect the brain. Primary bile acids are obtained from cholesterol in the liver and linked with glycine or taurine. Secondary bile acids are modified by bacteria in the gut. They play an important role in the breakdown and absorption of fatty substances. But as I said, they can also affect the brain.
Two studies in mice found that stress and social disturbances reduce the production of bile acids by the gut bacteria and change the genes involved in their production.
Your gut-brain axis is also connected via the immune system. The gut and gut microbes play an important role in your immune system and inflammation by controlling what passes into the body and what is excreted.
If your immune system is turned on for too long, it can lead to inflammation, which is associated with a number of brain diseases such as depression and Alzheimer's disease.
Lipopolysaccharides (LPS) are molecules consisting of fatty acids (lipids) and complex carbohydrates (polysaccharides). They occur on the surface of gram-negative bacteria. The immune system recognizes bacteria with the help of LPS, and free LPS therefore provokes a strong immune reaction. Lipopolysaccharide (LPS) is an inflammatory toxin produced by certain bacteria. It can cause inflammation if too much of it passes from the gut into the blood. This can happen when the intestinal barrier becomes leaky so-called. leaky gut, which allows bacteria and LPS to pass into the blood.
Inflammation and high levels of LPS in the blood have been associated with a number of brain disorders including major depression, dementia and schizophrenia.
Gut bacteria affect brain health, so by changing your gut bacteria you can improve your brain health. Probiotics are live bacteria that provide health benefits if eaten. But there are different types of probiotics. Probiotics that affect the brain are often called "psychobiotics" . Some probiotics have been shown to improve symptoms of stress, anxiety and depression.
A small study of people with irritable bowel syndrome (IBS) and mild to moderate anxiety or depression took a probiotic called Bifidobacterium longum NCC3001 for six weeks, which in the study significantly improved symptoms.
Prebiotics, which are usually fibers fermented by your gut bacteria, can also affect brain health. One study found that those who ate a prebiotic called galacto-oligosaccharides for three weeks significantly reduced the amount of the stress hormone (cortisol) in the body.
Probiotics that affect the brain are also called psychobiotics. Both probiotics and prebiotics have been shown to reduce levels of anxiety, stress and depression.
Did you know that certain foods can help you think more clearly and protect your memory? A few groups of foods are particularly beneficial for the gut-brain axis.
Here are some of the most important:
The gut-brain axis refers to the physical and chemical connections between your gut and your brain. Millions of nerves and neurons run between your gut and your brain. Neurotransmitters and other substances produced in your gut also affect your brain.
By changing the types of bacteria in your gut, it may be possible to improve your brain health.
Omega-3 fatty acids, fermented foods, collagen with prebiotics , probiotics, and polyphenol-rich foods can improve your gut health, which can benefit the gut-brain axis.
