What is your gut-brain connection and what role does nutrition play?
The gut-brain connection is a two-way communication system between your gut and your brain.
It’s a complex network of nerve cells, chemicals, and microbes, and it's the reason your body produces stomach juices when you think about food or why you may get stomach cramps when you're stressed.
The gut-brain connection links your central nervous system (CNS), including your brain, with the enteric nervous system (ENS) in your gut. Often dubbed the “second brain,” the ENS plays an important role not only in your digestive health but also in your mental health.
There are both physical and chemical connections between your gut and your brain, involving:
The vagus nerve: a large nerve that runs from your brain to your colon.
Neurotransmitters: chemical messengers that help regulate digestion and emotional well-being.
The gut microbiome: an ecosystem of trillions of bacteria and other microorganisms that live in your gut and are important for your health.
Although it’s a relatively new area of research, there’s increasing evidence that improving the health of your gut microbiome could help reduce symptoms of mental health conditions like anxiety and depression.
Some studies also suggest that your diet can affect your mental health. The ZOE at-home test uses the latest science and technology to analyze your gut microbiome and helps you find the best foods for your gut and your metabolic health.
The gut-brain connection
The gut-brain connection is a complex two-way communication network involving your nervous system, your immune system, and the system of chemical messengers known as neurotransmitters.
Your unique gut microbiome plays a part in all of these.
The vagus nerve
The vagus nerve is a large nerve that runs from your brain to your colon, physically connecting your gut to your brain.
Research involving both animals and people has found that the vagus nerve plays a crucial role in carrying signals between the gut and brain.
Animal studies also suggest that the gut microbiome, which produces substances that can influence mood, is involved in this.
A study in mice showed that feeding the animals probiotics — living “good” gut bacteria — reduced the levels of stress hormones in their blood. But after the vagus nerve was cut, this no longer happened.
Other research suggests that a similar relationship may exist between stress, the gut, and the vagus nerve in humans.
One study found that people with Crohn’s disease or irritable bowel syndrome (IBS) had higher markers of stress and reduced vagus nerve function, compared with people without these conditions.
Neurotransmitters and the gut microbiome
Neurotransmitters are chemical messengers involved in a variety of functions in your body. They are produced in both your brain and your gut and are another part of the gut-brain connection.
Your gut microbiome can influence the production of some neurotransmitters. These include serotonin and gamma-aminobutyric acid (GABA), which are both important for your emotional well-being.
Your gut produces a large proportion of your body’s serotonin, and studies have shown that your microbiome helps regulate this.
In your gut, serotonin plays a role in processes including digestion. However, the changes serotonin makes in your gut may also send signals to your brain that affect the production of neurotransmitters there. In the brain, serotonin is involved in mood and sleep.
Your gut bacteria also produce the neurotransmitter GABA, which helps reduce stress, anxiety, and fear. Some animal studies have shown that boosting “good” gut bacteria with probiotics can increase the production of GABA.
The gut microbiome and the immune system
The immune system is your body’s protection against disease. It’s a network of cells, chemicals, and organs that work together to fight harmful bacteria, fungi, and viruses.
It is also a crucial component of the gut-brain connection. Just as your immune system can impact your gut health, your gut microbiome can directly affect your immune system.
A large proportion of your immune system is actually found in your gut.
Although there’s still a lot to learn about how gut microbes affect the immune system and brain function, scientists know that the bacteria in your gut can influence the level of proteins called cytokines.
These proteins are essential to your body’s inflammatory response and can affect brain function.
Gut health and mental health
Although both gut health and mental health are complex, there’s an increasing amount of evidence that they can influence each other.
Scientists have identified specific gut microbes that may be connected with mental health conditions.
One study found that people with depression had fewer of two types of bacteria called Dialister and Coprococcus in their guts. Study participants with more of these bacteria reported higher scores when researchers asked them about their quality of life.
Scientists have also seen some encouraging results when investigating the use of fecal microbiota transplants (FMT) as an experimental treatment for mental health conditions.
FMT uses samples of poop containing bacteria from one person’s gut microbiome, which researchers transplant into another person’s gut.
Several studies have shown that FMT from donors without mental health conditions improved symptoms in people who had depression and anxiety, although in many cases the symptoms returned a few months after the treatment had ended.
Diet, probiotics, and mental health
There’s some evidence that improving what you eat can help with your mental health.
One study also found that people with depression saw improvements in their symptoms after changing their diets based on personalized advice from a nutritionist.
Meanwhile, diets consisting mostly of foods that cause inflammation in the body, such as fast food and processed foods, have been linked to symptoms of depression — although it’s not yet possible to say for sure that these diets are the direct cause.
Researchers are continuing to look into the potential benefits of probiotics for mental health, a field known as “psychobiotics.” Probiotics are live bacteria found in many fermented foods that may improve gut health.
Scientists studying over 700 people who were prone to anxiety found that eating fermented foods containing probiotics was linked to fewer symptoms of social anxiety.
There are many probiotic supplement products. However, it’s unclear how much these can help with your mental health.
A recent review of 21 studies looked at the effect of probiotic supplements and other dietary changes on people’s anxiety symptoms. It found that although probiotics helped in some cases, non-probiotic approaches were more effective.
Another analysis of 14 studies had similar results.
At ZOE, we know that fermented foods containing probiotic bacteria are good for your gut health. Eating these foods in small amounts daily can help these "good" bugs to stick around.
Probiotic-rich foods include:
cheeses such as aged cheddar, parmesan, and Swiss cheeses
It’s also important to feed your gut bugs with prebiotics. You can read about foods that contain prebiotics here.
There is plenty of science showing that probiotic and prebiotics foods are good for your gut health. At ZOE, we run the largest nutrition and gut microbiome study in the world, with over 10,000 participants so far.
Our research shows that there is no one-size-fits-all answer to nutrition and that everyone’s microbiome and the way they respond to food is unique.
Eating the right foods for your body can improve your gut health.
Not sure where to start? The ZOE program can tell you which of the 15 “good” and “bad” gut bugs that we’ve identified live in your gut and which foods are your personal “gut boosters” and “gut suppressors.”
Unpublished research found that 82% of people who closely followed their gut-friendly ZOE personalized nutrition program said they had more energy after 3 months.
The gut-brain connection is a complex, two-way communication system between your gut and your brain. It involves your immune system, chemical messengers called neurotransmitters, and a direct physical connection via your vagus nerve.
Your gut microbiome also plays a significant part in much of this communication, including by influencing the levels of hormones, neurotransmitters, and proteins in your body.
Research suggests that your gut microbiome may influence mental health conditions like anxiety and depression. Scientists have identified specific types of bacteria that may be involved.
High-quality diets, including those with foods containing probiotics and prebiotics, can improve your gut health and may help to boost your mood.
Finding the best foods for your gut starts with an understanding of the unique makeup of your gut microbiome.
The ZOE at-home test analyzes the bugs that live in your gut, in combination with your blood sugar and blood fat responses. Using the latest science, the ZOE program helps you pick the best foods for your “good” bugs and your metabolic health.
Anxiety and IBS revisited: ten years later. Clujul Medical. (2015).
A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Medicine. (2017).
A review of dietary and microbial connections to depression, anxiety, and stress. Nutritional Neuroscience. (2018).
Effect of fecal microbiota transplant on symptoms of psychiatric disorders: a systematic review. BMC Psychiatry. (2020).
Effects of regulating intestinal microbiota on anxiety symptoms: A systematic review. General Psychiatry. (2019).
Gut/brain axis and the microbiota. The Journal of Clinical Investigation. (2015).
Gut feelings: the emerging biology of gut-brain communication. Nature Reviews Neuroscience. (2011).
Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell. (2015).
Ingestion of lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences of the United States of America. (2011).
Leaky gut biomarkers in depression and suicidal behavior. Acta Psychiatrica Scandinavica. (2018).
Magnetic resonance spectroscopy reveals oral Lactobacillus promotion of increases in brain GABA, N-acetyl aspartate and glutamate. NeuroImage. (2015).
Microbiota-immune interactions: from gut to brain. LymphoSign Journal. (2020).
Neurotransmitter modulation by the gut microbiota. Brain Research. (2018).
Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers. Psychopharmacology. (2015).
Relationship between vagal tone, cortisol, TNF-alpha, epinephrine and negative affects in Crohn's disease and irritable bowel syndrome. PloS One. (2014).
Serotonin, tryptophan metabolism and the brain-gut-microbiome axis. Behavioural Brain Research. (2015).
The anxiolytic effect of probiotics: A systematic review and meta-analysis of the clinical and preclinical literature. PloS One. (2018).
The ever-changing roles of serotonin. The International Journal of Biochemistry & Cell Biology. (2020).
The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology. (2019).
The neuro-endocrinological role of microbial glutamate and GABA signaling. Frontiers in microbiology. (2016).
The role of gut microbiota in immune homeostasis and autoimmunity. Gut microbes. (2012).
The vagus nerve at the interface of the microbiota-gut-brain axis. Frontiers in Neuroscience. (2018).
Vagus nerve as modulator of the brain-gut axis in psychiatric and inflammatory disorders. Frontiers in Psychiatry. (2018).