“All disease begins in the gut.”
Your gastrointestinal tract (your gut) is tightly connected to your brain, and as a result, what you put into your body can affect how you physically feel and how you mentally feel. The gut, just like the brain, has one unique signaling system that relies on receptors and signals to help the gut function and relay messages to and from the brain. The gut’s nervous system is known as the enteric nervous system, and the communication between the brain (central nervous system) and the gut is known as the gut-brain axis. If it had to, the enteric nervous (ENS) system could function independently of the brain’s central nervous system (CNS.) The enteric nervous system is often referred to as the “second brain.”
What is the gut microbiome?
Approximately 100 trillion microbes (tiny organisms such as bacteria) from a thousand diverse species live in the human gut. This is known as the gut microbiome. The gut microbiome serves many essential roles in our overall health, including our gut health and our brain health. While the human genome consists of roughly 25,000 genes, the microbes in your gut express about 3 million unique genes. Many of these bacterial genes help build molecules that let you digest food, keep harmful gut bacteria away, and even feel emotions. Food and other dietary sources that we put into our bodies can dramatically impact the quality of microbiome content in our gastrointestinal system, which can significantly contribute to how we feel daily. The study of gut microbiota affecting mental health is a relatively new research topic gaining popularity these past years.
Taking a look at the research between bacteria and mood
Research shows that individuals with depression and other mental health disorders have very different gut microbiomes from those who don’t have these conditions.
One study found that the bacteria Coprococcus seems to have a pathway related to dopamine, one of the vital brain signals involved in mood regulation and is linked to depression. However, this study did not have evidence of exactly how this might protect against depression. The same microbe also makes an anti-inflammatory substance called butyrate, and increased inflammation is known to be linked to depression.
Some bacteria in the Clostridium genus produce propionic acid, which can reduce your body’s production of mood-boosting dopamine and serotonin. Other species produce the amino acid tryptophan, a precursor to mood-balancing serotonin.
A survey of small-scale controlled trials found that Bifidobacterium and Lactobacillus (types of probiotics) strains improved depressive symptoms overall, while other studies show similar effects on anxiety. One Australian study published in 2017 even suggests that a diet higher in beneficial bacteria can banish depression in more than a third of people.
The gut-brain connection
Neurotransmitters are chemical signals that are made in the brain and the body and send signals to the brain for processes throughout the body to work. Neurotransmitters that are known to affect our mood include dopamine, serotonin, and norepinephrine. The majority of the neurotransmitters that work in the brain are initially produced in the intestines. For example, the enteric nervous system can produce and store approximately 90% of our total serotonin and 50% of our total dopamine.
Gut microorganisms can affect the gut in three ways which include the following:
- Vagus nerve: Some gut microbes “talk” with the brain through the vagus nerve, which connects the intestines with the brain, sort of like a superhighway. Some gut bacteria can play a role in deactivating or activating the neurons that send signals through the vagus nerve to the brain.
- Enteric nervous system: Certain metabolites (breakdown of products) affect the brain cells that control gut function.
- Bloodstream: Gut bacteria produce and release specific metabolites that enter the blood circulation and interact with our immune system. Gut bacteria can change which neurotransmitters are in the bloodstream.
Probiotics for mental health?
Probiotics have been popular for “gut health” for years, and some researchers are curious whether certain probiotics can affect your mood regulation, hence coining the term “psychobiotics.” The theory is that people with depression, anxiety, or other mental health issues would routinely have their gut microbiomes sequenced to determine which types of microbial genes they are carrying. Then, individuals with high levels of bacteria tied to poor mental health, or low levels of bacteria that healthy people have in abundance, could receive a tailored probiotic to fix the imbalance. Of course, this is a proposed idea. The next step would be clinical trials to show whether microbes or microbial cocktails can boost mental well-being beyond the placebo effects commonly found in many psychiatric treatment studies.
Major depressive disorder
Major depressive disorder is a type of mood disorder that is characterized by depression that affects everyday life for at least two weeks in duration. Individuals with depression often experience anxiety. Nearly one-half of those diagnosed with depression are also diagnosed with an anxiety disorder. Depression is marked with feelings of despair and sadness, and many individuals who struggle from depression cannot find a concrete reason why they are feeling this way. On the other hand, there are many underlying triggers associated with depression. These include substance use disorder, extreme stress, past traumas, and anxiety. Like other mental health disorders, signs and symptoms of depression can be minimized with medication, psychotherapy approaches, or both. However, if left untreated, depression can lead to suicidal thoughts or attempts and substance use disorders to cope with the empty feelings associated with depression.
Signs and symptoms of depression:
- Depressed mood, such as feeling sad, empty, hopeless, or tearful
- Marked loss of interest or feeling no pleasure in activities
- Weight gain or loss
- Insomnia or sleeping too much
- Fatigue or loss of energy
- Feelings of worthlessness
- Poor concentration
- Decreased ability to think or concentrate, or indecisiveness
- Suicidal thoughts or attempts
Until researchers are able to prove the specifics about how gut bacteria can help or worsen depression through clinical trials (which most likely will take a few years); psychotherapy with or without medication is the best treatment approach we have. If you or a loved one is struggling with signs of depression, AKUA Mind and Body can help.