We have been aware of the connection between our guts and our moods for a long time: phrases like “gut reaction” were around long before science started to explain how that might be happening. Recently there’s a whole new area of research into psychobiotics: probiotics that have been found to benefit our brains!
We know a lot of information flows between our digestive systems and our brains, collectively called the gut-brain connection. That communication flows both ways. We used to think that allowed the brain to run the gut properly. We now know that the vast majority of communication is from the gut to the brain, rather than from the brain to the gut. This is why the gut is often referred to as the “second brain”.
Psychobiotics is the term for the live bacteria that benefit mental health through interaction with our resident gut bacteria: they influence the relationship between bacteria and brain. Psychobiotics can exert anxiety-reducing and antidepressant effects, changing emotional, cognitive, and general health.
Microbial diversity in the gut is essential for so many normal physiological functions, not just of the gut, but of many organs, including the brain. Different probiotics are being studied for their different benefits on mood and behaviour, with promising results.
Effects on mood and behaviour: Pathogenic (bad) bacteria in the gut can induce negative behavioral and psychological changes in humans and animals. Some probiotics have been shown to help reverse these, and to improve anxiety and depression.
Probiotics can also have a beneficial effect on gut symptoms, such as abdominal pain or nausea, often seen in people experiencing chronic stress or depression.
One aspect of the gut-brain connection is the production of neurotransmitters by your gut microbiome. Neurotransmitters enable information to be transmitted between neurons (brain cells). It may surprise you to learn that most neurotransmitters are made by the microbes in our guts, not in our brains.
These neurotransmitters are:
Serotonin, associated with happiness, motivation, and feeling calm
Dopamine, associated with a sense of reward, positive affect (facial expression), and extraversion. It is reduced by lack of social interaction, and triggered by receiving a smile 😄
GABA, short for gamma amino butyric acid, gives feelings of relaxation, ability to focus, and helps us sleep through the night. It also decreases inflammation
Acetylcholine, associated with the formation of memories, also promotes a feeling of calm and regulates anxiety
You can see why we feel better when we are making enough of all of these, and why if we lack them, we may feel out of sorts!
Many modern antidepressants work by making our serotonin work harder for us. But why should so many people seem to need more of serotonin’s effects? Could it be because their gut microbiota aren’t making enough?
Reduced depression: Significant improvements in depression have been seen after 4-8 weeks of probiotic use, with no side effects.
Brain derived neurotropic factor, or BDNF (likened to “Miracle-gro” for the brain), was seen to increase at the same time as depression decreased. As BDNF is helpful for healing our brains, it may be an important factor in this.
Both anxiety and depression are associated with chronic low-grade inflammation. This inflammation is often low enough that people are not aware of it, or don’t know how to deal with it.
Here’s where psychobiotics can come to the rescue!
Bad bugs and bad diets trigger the gut to make inflammatory chemicals called cytokines. These include IL-6, TNF-alpha and IL-I beta. They can trigger anxiety, depression, fatigue, pain and hostility. And they can adversely affect your memory, likely due to neuro-inflammation (that’s right, a mildly inflamed brain!)
These cytokines also increase production of kynurenin, a chemical that induces anxiety-like behaviour in a dose dependent manner: the more you make, the more anxious you are likely to feel. And because stress increases gut leakiness, this can become a vicious cycle.
Probiotics reduce circulating cytokine concentrations, and many of them, including the bifido bacterium and lactobacillus species, help heal a leaky gut.
Protecting your brain: The gut microbiota also regulate the integrity of the blood-brain barrier (BBB). This is a tight barrier between your bloodstream and your brain, that protects your precious brain from chemicals that could impair its function. A leaky blood-brain barrier is akin to a leaky gut. Indeed it is often the inflammatory cytokines made by a leaky gut, that make their way to the brain and cause problems there too.
When the BBB is impaired, unwanted chemicals can get into the brain, and trigger the brain’s immune response, and even more inflammation.
Psychobiotics help restore the blood brain barrier, after inflammation has caused it to become more permeable.
Oxytocin, the “Love Hormone”: One strain of probiotic has been shown to increase production of oxytocin, a hormone we make that triggers feelings of bonding and connection. Oxytocin has been called the love hormone: we make lots of it when hugging or making love, or breastfeeding. It triggers warm and fuzzy feelings of relaxation, trust, and overall psychological stability.
The human body is an ecosystem, with complex interactions between all the different parts. If the gut microbiome is significantly out of balance it can affect many other areas. Fortunately, promoting a healthy gut microbiome can be as simple as eating a wide variety of the right foods, see (Count Plants Not Calories) or taking the right probiotic supplement to support our gut microbiome. That microbiome can then help our digestion, our brain and our moods. This can make our lives happier, and the lives of those we interact with.