We all have trillions of microbes living in our intestines. This microbiome, which develops in infancy, plays a major role in our digestion, but there’s growing evidence that it affects more than just our digestive system.
Role of the microbiome
This collection of critters weighs about 2 kg and includes bacteria, fungi, and viruses. There is no “normal” microbiome composition, but the more variability there is, the better it is for our health. What’s hanging out inside of us has a lot to do with what we eat, but it’s also affected by other factors, including stress and antibiotic usage.
What’s in our gut also influences what’s going on in our brain. Some gut bacteria may stimulate the vagus nerve, which connects the gut and brain. Much of our serotonin is produced in the gut, and the microbiome plays a role in that. Besides being transformed into serotonin, tryptophan can also be transformed into a neurotoxic substance, and the microbial mix may plays a role in determining how much tryptophan goes to each pathway.
The microbiome appears to play a role in inflammation through a few different potential mechanisms, and depression and some other mental illnesses are thought to have an inflammatory component. Taking probiotics can help to reduce the levels of inflammatory markers in the blood.
One study found that overgrowth of a particular Candida species (a yeasty beastie) could contribute to the development of autism. Disruptions in the microbiome may also have a role in schizophrenia, mood disorders, and anxiety disorders.
What do we do about it?
Dietary fibre is important to consume, as it provides food for certain helpful types of bacteria. Diets high in fibre have been linked to a decreased risk for depression and anxiety. Diets high in antioxidant and phytonutrients (micronutrients found in plants) help to promote greater diversity in the microbiome.
While taking probiotics may be beneficial, it’s not clear what specific composition of species or what dose would be most effective. Another option that’s being trialled is fecal microbiota transplants, something that’s currently used for treating recurrent C. difficile infections. The University of Calgary is doing studies with a pill version (a pill o’ poop, if you will?), while Johns Hopkins University does it via colonoscopy for C. diff.
Interesting stuff, although I don’t imagine many people would be signing up for the pill o’ poop anytime soon. A few years ago I took probiotics regularly for maybe a year or so after I picked up a Giardia infection while travelling, which wreaked extended havoc on my gut. I don’t recall noticing any link to my mental health. I could certainly eat better than I do, but I don’t care sufficiently to do anything about it.
Do you think your gut and your brain are chatting?
- American Society for Microbiology (2020): Of Microbes and Mental Health: Eating for Mental Wellness
- Clapp, M., Aurora, N., Herrera, L., Bhatia, M., Wilen, E., & Wakefield, S. (2017). Gut microbiota’s effect on mental health: the gut-brain axis. Clinics and practice, 7(4), 131-136.
- Rea, K., Dinan, T. G., & Cryan, J. F. (2020). Gut microbiota: a perspective for psychiatrists. Neuropsychobiology, 79(1-2), 50-62.
- Science Magazine (2020): Meet the ‘psychobiome’: the gut bacteria that may alter how you think, feel, and act
- University of Calgary (2019): Is mental health a gut feeling? How your microbiome may or may not affect your mental health