Are the bacteria in your gut making you sad?

Emerging research linking bacteria in the human gut to mood and psychiatric disorders like depression and anxiety could shake up the way we approach treatment for psychiatric conditions (we could use food, specifically fermented food, to become happier!). There are more bacteria in our bodies than human cells and more than 1000 species and 7000 different strains.

To give you some background, the gut-brain axis refers to the communication system between the gut and the brain. The gut and brain communicate via hormones, nerves, and the immune system. Recent research supports the theory that the gut-brain axis plays a role in the development and function of the brain and in stress response.

Studies show that the microbiome, a term used to describe the bacteria and other microorganisms (including yeast and parasites) that call our guts home, is key to the development of the nervous system and behavior. In unpublished experiments, researchers found that mice that are stressed early in pregnancy show reduced Lactobascillus in their vaginas, and their pups exhibit the same changes in their guts. In their brains, the offspring have decreased availability of several amino acids related to nerve communication.

We could use food, specifically fermented food, to be happier people!

Furthermore, in an autism study out of the California Institute of Technology, microbiologist Sarkis Mazmanian and colleagues modeled the disorder in mice by injecting pregnant animals with a chemical that mimicked a viral infection. The resulting offspring showed autism-like symptoms, such as increased anxiety-like behaviors, decreased social tendencies, and abnormal, repetitive movements. The mice also had leaky guts, which have been reported in some studies of humans with autism. Feeding the mice a particular strain of the human gut microbe, Bacteroides fragilis, repaired their guts and improved the behavioral symptoms, suggesting that there is a link between autism and the microbiome.

Dysbiosis is an imbalance in the gut bacteria, often with an overgrowth of unhealthy bacteria and too few of the healthy bacteria. Inflammation of the gut lining often goes hand-in-hand with dysbiosis and when the gut is inflamed, it can become “leaky”, hence the term “leaky gut”. The spaces between cells become big enough for bacteria, components of bacteria, and undigested food particles to enter the bloodstream, which can trigger an immune response and cause even more inflammation. Increased immune cells in the body can also cause an amino acid, L-tryptophan, to be converted TRYCATs instead of seretonin, a neurotransmitter thought to be a contributor to feelings of well-being and happiness. TRYCATS can drive changes in behavioural responses, including the induction of anxiety and depression. 

On the flip side, an individual’s social environment can also influence their physiology. A recent study showed that social stress can increase the number of receptors that bind LPS (lipopolysaccharide), a component of the external membrane of certain gut bacteria that enters the bloodstream when the gut is leaky. So, stress can increase our sensitivity to the harmful effects of leaky gut, and in turn, leaky gut can make us  more stressed due to mood disturbances. Where does it end!?

Well, there are a few simple steps we can take to maintain healthy gut bacteria:

Include fermented foods in your diet! Good options are sauerkraut, kombucha, Kim chi,  water or dairy kefir, and plain yogurt. The fewer additives, added sugar, and flavouring, the better. A single serving of strawberry flavoured greek yogurt can have more than 2 teaspoons of sugar in it. This sugar also binds water, making it less available to bacteria, which decreases the number of healthy bacteria in the yogurt.  As well, try not to cook your fermented foods; it will kill a lot of the healthy bacteria. 

You can also add a high-quality probiotic supplement to your regime. The supplement should include the following bacteria: L. acidophilus, B. longum, and B. bifidum (all strains of bacteria that have been shown to be linked to a healthy microbiome). Chat with a health care practitioner you trust for a recommendation!  

Finally, to the best of your ability, reduce or manage your level of stress (or how you view and deal with stres). This Ted Talk can help reshape how you think of stress! To reduce the impact stress has on your life, you can also make sure you are getting enough sleep (all lights off, cellphone on airplane mode), exercise regularly - in ways that you actually enjoy, and make an effort to nurture your social connections. Check out the work of Shawn Anchor to learn more about being happy. 


For more information on finding a great probiotic for your needs, check out this guide: for more information on finding a great probiotic for your needs, check out this guide:

1. Martin-Subero, M., Anderson, G., Kanchanatawan, B., Berk, M., & Maes, M. (2015). Comorbidity between depression and inflammatory bowel disease explained by immune-inflammatory, oxidative, and nitrosative stress; tryptophan catabolite; and gut–brain pathways. CNS Spectrums21(02), 184–198. 

2. Dinan, T. G., & Cryan, J. F. (2016). Mood by microbe: Towards clinical translation. Genome Medicine8(1), .

3. Shen, H. H. (2015). News feature: Microbes on the mind. Proceedings of the National Academy of Sciences112(30), 9143–9145.

4. Hsiao, E. Y., McBride, S. W., Hsien, S., Sharon, G., Hyde, E. R., McCue, T., Mazmanian, S. K. (2013). Microbiota modulate behavioral and physiological abnormalities associated with Neurodevelopmental disorders. Cell155(7), 1451–1463. doi:10.1016/j.cell.2013.11.024