top of page
  • Dr. Sarah Penney, ND

What Science Says: Gut Bacteria and Mood

Updated: Feb 10, 2020

The role that healthy gut bacteria play in keeping the body in balance is not a new concept in Naturopathic medicine, but research is starting to accumulate showing specific links between digestive health and mood. We have billions of bacteria in our gut, just as many tiny bacteria as we have cells in our body, and as it turns out they play an important role in the stability of our happy hormones and levels of inflammation. As we grow and age life factors like antibiotic use, viral infection or even stress and nutritional choices can all affect these bacteria, and may play a role in certain health concerns.


Over the last 10 years research has clearly demonstrated that gut health and bacterial balance is linked to behaviour and mood in animal models. The proposed pathway by which gut bacteria affects mood is through a molecule called GABA, which is a neurotransmitter in the brain that that has a calming and soothing effect. Good gut bacteria has been shown to both increase GABA levels and enhance the receptors for GABA to amplify this effect, which may be helpful in anxiety. Supplementation of good probiotic bacteria in mice has also been shown to lower levels of a stress hormone similar to cortisol (a fight or flight hormone that is high in anxiety and depression). These mice also demonstrated a reduction in stress-related activities. (1) Sounds like one happy group of research mice, which is nice to hear!

But you are probably not a mouse, so let's look at the available human research on bacterial balance and mood. A recent review of all the evidence to date about probiotic supplementation and depression and anxiety was published in September 2016. Researchers identified 10 clinical trials on this topic to analyze, all looking at supplementation of probiotics in capsule, powder or yoghurt form and resulting changes in mood. Six of these studies look at ‘healthy’ individuals with diagnosed anxiety/depression, and 4 of them looked at participants who were also diagnosed with cancer, IBS or a major depressive disorder. Researchers commented that these studies used a variety of probiotic strains with different doses for varying durations, which made the results hard to compare. Five out of 10 studies showed a significant improvement in symptoms of anxiety and depression after probiotic use compared to placebo treatments, and several other showed improvements that did not reach statistical significance. Researchers concluded that this preliminary evidence supports the use of probiotics in treatment of these conditions and that this link should be investigated further. (2)


The options for probiotic combinations seem endless for some patients, and not all strains will give you the same results. Lactobacillus and Bifidobacterium are the two main categories of probiotic bacteria that can be taken in supplement form, and there are multiple strains of bacteria within each genus that have different actions. Of the studies reviewed that demonstrated improvements, the strains of probiotics that were used included Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus helveticus, Lactobacillus rhamnosus, Bifidobacterium bifidum, Bifidobacterium longum, Bifidobacterium lactis and Bifidobacterium breve. Doses ranged from 2 billion to 40 billion CFU (colony forming units) per day. (2) When selecting a probiotic product, I always look for one that has been refrigerated because probiotics are live bacteria and any kind of heat and moisture can easily destroy them. Some probiotics have been treated to improve their chance of being shelf stable at room temperature, but the bacteria contained will still die off over time so I like refrigerated products to get the best dosage for your dollar.

Balancing gut bacteria is one tool that I consider trying in patients suffering from anxiety or depression, but in my experience results to depend heavily on the root cause of the issues in each individual patient. Not everyone will be suffering from mood disorders due to an imbalance like this, but as a naturopath I do more detective work to decide if it might be a contributing factor. There are lots of ways you can keep your gut bacteria happy for overall help anyhow– by consuming probiotic foods, eating lots of fibre, decreasing your stress and even getting good quality sleep! Book an appointment for more info or for a personal assessment!

Dr. Sarah Penney, ND, MSc




198 views0 comments

Recent Posts

See All
  • Instagram
  • c-facebook
  • YouTube


bottom of page