Scientists have found several links between our gut bacteria and brain health that might change treatment options for mental disorders in the future. Many struggle with depression and related illnesses for which antidepressants or mood stabilizers have not been effective. For others, these treatments cause severe side effects. For such people, focusing on gut health may bring much-needed relief.

This research is still ongoing and cannot guarantee a “cure” for depression. However, the latest news about how poor gut bacteria can lead to depression shows some promise in how we approach mental illness.

Doctors Explain How Poor Gut Bacteria Can Lead to Depression

The impact of our microbiome on the immune system, brain development, and behavior have been the subject of much research in recent years.  In 2015, 90% of the more than 4,000 articles published on the subject published within the previous 5 years.  This makes it a rather recent correlation in the field of psychology and biology as it relates to humans.  Much of this research is still being conducted in the lab through clinical observations and animal trials.

Essentially scientists have discovered strong evidence of a connection between the gut and the brain. This is created while we are still in the womb, but the effects remain throughout our lifetime.  The microorganisms that live in our gut are in constant communication with the gut and immune system cells.  This communication creates an interaction for the development of many neuropsychiatric and metabolic disorders, with autoimmune disorders being the most prevalent.

Essentially, if a mother had poor gut health while pregnant, then it created a deficiency in the formation of certain systems in the fetus. Unfortunately, these systems are instrumental in neuropsychology development, as well as immune and endocrine system operation. Basically, having proper gut health in the beginning stages of life is out of our hands; however, we can alter it by changing our diet once we have freedom to do so.

Our Healthy Friends

These microbiomes, or “gut bacteria,” have been essential links to the progress of humans throughout our evolution. Originally, our more than 1,000 species and over 7,000 subspecies of gut microbiota had been producing metabolites and nucleic acids in the gut and transporting them into our circulatory system. This triggered various inactive genes which were designed to benefit our health and disease evolution.

This led to nicknaming the microorganisms our “healthy friends,” which later on led to the Healthy Friend hypothesis. This hypothesis came about in 1989 with the observation that there was an increase in allergic diseases and autism in more developed countries.  The hypothesis states that developed countries tend to be more hygienic by using antibacterial sprays and antibacterial hand washes and have made more changes in their diet, creating a change in our relationship with our “healthy friends.”

Gut-Brain Connection to Mental Health

It is relatively easy to understand how our “healthy friends,” or gut bacteria, can affect our immune system and resistance to diseases. However, how exactly does gut bacteria influence mental health?  As mentioned above, we have thousands of microorganisms tasked with creating benefits leading to our evolution.  Of those thousands of microorganisms, some were tasked with aiding in the creation of certain hormones related to our mental abilities and health.

Here is a list of some gut bacteria and how they relate to our mental wellbeing:

Lactobacillus and Bifidobacterium synthesize gamma-aminobutyric acid (GABA) from monosodium glutamate.  GABA is a neurotransmitter that blocks impulsive nerve cells in the brain.  Low levels are associated with anxiety and mood disorders.

Escherichia coli, Bacillus, and Saccharomyces produce norepinephrine. Norepinephrine is a chemical in the brain and body that acts as a hormone and neurotransmitter.  Its function is to prepare the brain and body for action in times of waking and various levels of stress.

Candida, Streptococcus, Escherichia, and Enterococcus produce serotonin.  Serotonin is also known as 5-HT and is referred to as the “happy chemical” since it plays a key role in maintaining mood balance.  It transmits messages between nerve cells and is involved in the synthesis of melatonin which helps balance our sleep cycle.

Bacillus and Serratia produce dopamine.  It is similar to serotonin and norepinephrine in that it is a hormone and neurotransmitter.  It is responsible for signaling a perceived pleasure from a desired outcome of an event.  The higher your dopamine levels, the higher your desire to do a certain activity, which raises its level.  It is often associated with addictions, but in its proper amount acts as an internal motivator.  It also has various other duties related to our nervous system, digestive system, and immune system.

Research on Gut Bacteria

When rats were given Bifidobacterium infantis orally, they saw an increase in plasma tryptophan levels. Tryptophan is necessary to aid in the production of serotonin, melatonin, niacin (vitamin B3), and other hormones.

Lactobacillus acidophilus increases the expression of cannabinoid receptors in the brainstem.  These receptors are involved in our sensations of appetite, pain, mood, and memory.

Conversely, germ-free (GF) rats had high plasma serotonin levels.  Having high levels of serotonin can lead to serotonin syndrome, which is toxic to the body. Antidepressants known as SSRI’s and MAOI’s are designed to increase serotonin levels through various methods but must be monitored to prevent too much of an increase.

The psychiatric field has been using medication for years to attempt to balance serotonin and dopamine levels in the brain to treat depression.  Unfortunately, many people on antidepressants or mood stabilizers still report having symptoms.   Additionally, the medications come with a lot of side effects which may make taking them a miserable experience.  Ironically, these very medications can also alter our gut health; then again, stress, poor diet, trauma, lack of sleep, and plenty of other factors influence gut bacteria as well.

Because of the increasing importance of gut health, healthcare professionals have recently started advising individuals who are on various types of medications to supplement with probiotics. Many people with mental disorders report having digestive problems such as diarrhea, constipation, abdominal pain, and bloating; probiotics help with these issues.  Now with this new research, perhaps all psychiatrists will advise to use them as a supplement to antidepressant or mood stabilizing medications as part of the treatment.

Are we ready for probiotics to be the next step in treatment for depression?

All studies on the connection between gut bacteria and depression have primarily been done through animal testing. However, a few years ago, John Cryan, a neuroscientist at the University College Cork, published the results of his experiments on humans.  He first did an experiment on mice using Bifidobacterium longum bacteria to see how it would influence stress levels; the results were positive.

gut bacteria leads to depression

To see if he could get the same results in humans, he took 22 men and put them through a series of stressful situations, such as immersing their hands in ice cold water.  They were then given the powder form of the bacteria which was dissolved in milk.  After 4 weeks of being on these probiotics, they showed an increased resistance to the cold water and ability to keep their hands in the water for longer periods.  They also showed an improvement on memory tests.

Before you decide to run out to your neighbor health or drug store, John Cryan does warn, however, that:

  • We don’t have any evidence that the probiotics sold in stores will have the same result as the ones in the lab.
  • No single probiotic provides a magical cure for depression or any other mental illness. Test results also point to the use of one probiotic helping in one area but causing a deficit in another. As he puts it, “There’s no one bug to rule them all.”

Cryan states that the best course of action is to eat a daily healthy diet low in fast food as a method of getting a variety of healthy bugs, or microorganisms, in your body.  Creating a lifestyle of eating healthy can help ensure a healthy communication between the gut and brain. Therefore, it can minimize the negative effects of having too few “healthy friends.”

Final thoughts

While the studies are not conclusive yet, they give hope for those who struggle with depression or mental illness.  Whether you are on medication or not, changing your diet produces a better environment for gut bacteria. This will improve the connection between your gut and brain. Plus, having a healthy diet and taking probiotics helps increase other healthy gut behaviors. The latest report for the gut-brain connection to depression still awaits a final conclusion. Still, the evidence thus far brings hope to those who suffer from mental illness.

After all, a healthy diet does wonders for your brain and body, so it’s no surprise that it might help ease symptoms of depression. You don’t have to overhaul your diet completely, just work to make small changes each day so you can enjoy a clearer mind and a healthier gut.