Does Gut Microbiota Influence Mental Health?
Ever wonder why they call a hunch or an instinct a “gut feeling”? The link between your intestines and your brain is a lot closer than you think, and the more we discover about the health of our gut, the more we discover about ourselves.
Imagine if a key to better mental health lies with what we eat and how we grow our intestinal flora. Can we possibly dissipate anxiety and lessen depression by tweaking the probiotics we take? Scientists are trying to figure that out.
The Gut-Brain Connection
First of all, in order to begin to understand how the bacteria in your gut could possibly affect your brain chemistry, let’s talk about how the brain and gut work together. The “gut-brain axis” connects the two systems both physically and biochemically.
This means there is a tangible nerve line called the vagus nerve that runs between them, and where they are not connected physically, they are connected by neurotransmitters, specific chemicals only found within the gut and the brain.
The vagus nerve starts at the base of your brain and ends at your colon. it helps stimulate your throat and keeps the digestive tract moving, from the esophagus on down. Plus, it helps slow your heartbeat when necessary.
It is the highway between your brain and your digestive tract, constantly sending and receiving information via the enteric nervous system, which is the 100 million or so nerve cells that line your entire digestive tract.
If there is something wrong in the brain, you could have gut issues like sluggish digestion or acid reflux. If there is something wrong with the digestive tract, you can have symptoms of anxiety and depression. Problems with the vagus nerve can also lead to fainting.
Along with the nerve connection, there are special neurotransmitters only found in the brain and the gut. These neurotransmitters, like serotonin, produce feelings of happiness and help regulate your body clock. We often think of serotonin as a brain chemical, but the majority of it is actually made in – you guessed it – the gut.
But it doesn’t stop there – your gut also makes a neurotransmitter called GABA which works to control feelings of fear and anxiety, plus short-chain fatty acids that help regulate appetite, and form the blood-brain barrier, which keeps most bacteria and toxins out of your brain tissue. These neurotransmitters also help metabolize bile and amino acids. The resulting chemicals also have effects on the brain.
The Bacterial Benefit
What does all of this have to do with the bacteria in your intestines? Everything. The bacteria are what help produce all of this chemistry. Their growth and function actually create the chemicals your body uses to make neurotransmitters.
Inside of your intestinal tract, teems trillions of bacterial, viral and fungal strains. Anywhere from 300-1,000 different types of flora are working in your body at all times. In fact, your microbiota (the bacteria in your gut) accounts for two to five pounds of your mass. You heard that right - a few pounds of you is literally bacteria, fungi, and viruses. Now you know what to blame the next time you miss weight.
Much of these strains are beneficial, but some can be harmful. At times, our intestinal health actually relies on a tenuous balance between the helpful and harmful bacteria. It can get pretty complicated.
What we know is keeping your microbiota happy, diverse, and flourishing affects your health in a positive way. Low diversity and diminished numbers lead to infection and inflammation, and, possibly, poor mental health on top of everything else.
The Mental Health Link
Let’s take another look at the enteric nervous system. Disorders of the intestinal tract can irritate the nerve cells that talk to the brain. If these nerve cells sense something is amiss, they will send alerts to the brain, which can cause symptoms of anxiety and depression.
Doctors often prescribe antidepressants to people with IBS and other digestive conditions, because those drugs can actually calm the nerve cells in the gut and improve symptoms in some patients. We have found that gut inflammation can have a profound effect on mental health.
And, conversely, mental health can have a huge impact on digestion and gut wellness. Some of the most common symptoms that go along with anxiety and depression are: nausea, constipation or diarrhea, stomach pain, and loss of appetite.
Even temporary issues in healthy people, like fear of public speaking, or heartbreak, or nervousness before a job interview or an exam, can cause butterflies in the stomach and the inability to eat. Sometimes it causes frequent trips to the bathroom.
We have known for a long time that the gut and the brain have a very connected relationship. But now we are starting to discover why.
In February, a new study was published in Nature Microbiology that concluded people with depression are missing two key strains of gut microbiota.
Jeroen Raes, a microbiologist at the Catholic University of Leuven in Belgium, and his team re-examined an earlier group of subjects they had used to map a normal human microbiome. This group consisted of 1,054 Belgians.
Within that group,173 of them had been diagnosed with depression or had low scores on a quality of life survey, so the team compared their microbiomes with the other participants who were happy.
The strains of Coprococcus and Dialister were depleted or missing in the people with depression, even after correcting for confounding effects of antidepressants. Meaning, the finding held up when they accounted for the things that might affect microbiota, like age, sex, or certain medications.
To be sure, the team looked at data from another study that consisted of 1,064 Dutch people. They found the same thing: the lack of Coprococcus and Dialister in seven subjects suffering from clinical depression. Not only that, but They also found the depressed people had an increase in bacteria implicated in Crohn's disease, suggesting inflammation may be at fault.
On the bright side, strains of Faecalibacterium and Coprococcus bacteria were associated with subjects who had a high quality of life. Coprococcus may share a pathway related to dopamine, a key brain signal that induces feelings of happiness, reward, and contentment. The same microbe also makes an anti-inflammatory substance called butyrate, which may protect from the increased inflammation we see in people with depression.
What Does This All Mean?
It’s tempting to say that we’ve found the answer to mental illness and the cure for depression, but we are a long way from that. While we can see two specific strains of microbiota missing in depressed populations, we don’t know if they are a cause or an effect of the disorder.
Nor do we do not know if certain microbiota can cross the blood-brain barrier or if they communicate via the enteric nervous system. In short, we simply don’t understand how, exactly, our microbiome effects our mood, only that it likely does.
Scientists and researchers are about to conduct more specific studies to pinpoint the mechanisms of the gut-brain axis and possibly find cures for both digestive diseases and mental illness. Microbiota mapping, fecal transplant trials, new medications, and Inflammation studies are all on the horizon.
Until then, the best thing we can do is to keep our guts as healthy as possible. How do we do that? By maintaining variety in our diet and consuming foods with probiotics and prebiotics. We should also invest in our mental wellbeing by trying to mitigate large stressors in our lives, meditating and seeking therapy when we need it.
Exercise is an activity that helps your body perform optimally and is a very effective depression fighter. One of the best things you can do besides making changes to your diet, would be to go for a walk, pick up some weights or find a physical hobby that can lighten your mood and keep your mind thinking clearly.
Foods That Improve Gut Health
To maintain a healthy gut, your diet should include these foods:
- Omega-3 fats: These fats are found in oily fish and also in high quantities in the human brain. Studies in humans and animals show that omega-3’s can increase good bacteria in the gut and reduce risk of brain disorders.
- Fermented foods: Yogurt, kefir, sauerkraut, and cheese all contain healthy microbes such as lactic acid bacteria. Fermented foods have been shown to alter brain activity.
- High-fiber foods: Whole grains, nuts, seeds, fruits and vegetables all contain prebiotic fibers that are good for your gut bacteria. Prebiotics can reduce stress hormone in humans.
- Polyphenol-rich foods: Cocoa, green tea, olive oil and coffee all contain polyphenols, which are plant chemicals that are digested by your gut bacteria. Polyphenols increase healthy gut bacteria and may improve cognition.
- Tryptophan-rich foods: Tryptophan is an amino acid that is converted into the neurotransmitter serotonin. Foods that are high in tryptophan include turkey, eggs and cheese.
The best thing to do if you are concerned about your digestive system or your mental health is to widen your diet and get moving. Seek a mental health professional or a gastrointestinal specialist.
Hopefully, science will catch up with us soon and give us some solid answers. But we can start on the path to both gut health and mental health, while we wait.