The Microbiome & Emotional Health

Kathy Wheddon Nutritional Therapist DipION

Two recent studies have given more weight to the evidence that the microbiome is linked to our emotions. The area of 'psychobiotics' (the relationship between our gut flora and our emotional health) is a growing field, and I have blogged before about how the microbiome affects how we think and feel. However, these two new pieces of research look specifically at the emotions of both fear and depression.

Within this article:

Anxious woman
Lack of friendly gut flora may play a part in phobias and other abnormal 'fear' responses

Gut flora and the emotion of fear

The first study, carried out at the University of Cork, used a mouse model to look at whether or not the fear response was altered in mice that were raised in a completely germ-free environment, and therefore had an under-developed microbiome.

The key piece of information to come out of the research was that, the amygdala, which is the area of the brain responsible for emotional ‘processing’, appears to be hyperactive in microbiota deficient subjects. This can lead to an exaggerated response to fearful memories, and therefore create a tendency towards phobias or post-traumatic stress disorders for example.

One of the lead researchers on this study, Dr John Cryan said:

“It is turning upside down how we might develop strategies for fear and anxiety. It is a very exciting time for us.’’

While more work is still needed to fully understand the mechanisms behind the relationship between the microbiota and fear responses, Prof Cryan said it was likely ‘’that key signals from the gut to the brain act as regulators of the fear response.’’

He added that: “We are very excited about this because it is probably one of the first direct links to fear pathways,” and “We now know that for normal fear responses we need to have appropriate microbes in our gut.”

Longer term implications

In the longer term the researchers are hoping that by using the information gained from this study that they can now work to develop either a probiotic or some kind of dietary intervention that can manipulate the microbiome in a positive way to help dampen down this hyperactive fear response.

Another of the researchers on the project, Dr. Gerard Clarke commented that:

“It is just the start; we are now searching for strategies to target the microbiome to generate novel efficacious treatments for anxiety disorders such as PTSD,”

New study backs probiotics for depression

The second new study, performed by researchers at McMaster University, Ontario1, recruited 44 adults all of whom had IBS with either mild to moderate anxiety or depression. The study participants were divided in to two groups. One group was given a daily dose of the probiotic strain Bifidobacterium longum NCC3001, and the other group were given a daily placebo.

Man with head in his hands
Research shows that probiotics can help with depression

After six weeks both groups were subjected to psychological analysis and also Magnetic Resonance Imaging of the brain. Results showed that 64% of participants in the probiotic group saw reduced depression scores of at least two points, compared to only 32% from the placebo group reporting the same improvements.

Additionally results from the MRI testing verified that reductions in depression scores were accompanied by changes in the area of the brain involved in mood regulation.

One of the study authors, Dr Premysl Bercik commented that:

'This opens new avenues not only for the treatment of patients with functional bowel disorders but also for patients with primary psychiatric diseases.'

Despite both of these studies being fairly small, they add to the growing amount of evidence suggesting that the microbiome plays a large part in our emotional wellbeing as well as our physical wellbeing.

Healthcare professionals may be interested to read the following blog in the Probiotic Professionals about two of the strains of probiotic bacteria that may impact on anxiety

Or, you may wish to take a look at our informative post on the gut-brain axis


  1. Gastroenterology. 2017 May 5. pii: S0016-5085(17)35557-9. doi: 10.1053/j.gastro.2017.05.003. Probiotic Bifidobacterium longum NCC3001 Reduces Depression Scores and Alters Brain Activity: a Pilot Study in Patients With Irritable Bowel Syndrome. Pinto-Sanchez MI, Hall GB, Ghajar K, Bercik P.
  2. Ke, S., Wang, XW., Ratanatharathorn, A. et al. Association of probable post-traumatic stress disorder with dietary pattern and gut microbiome in a cohort of women. Nat. Mental Health 1, 900–913 (2023).
  3. Patterson E, Griffin SM, Ibarra A, Ellsiepen E, Hellhammer J (2020). Lacticaseibacillus paracasei Lpc-37® improves psychological and physiological markers of stress and anxiety in healthy adults: a randomized, double-blind, placebo-controlled and parallel clinical trial (the Sisu study). Neurobiol Stress. 13:100277. doi: 10.1016/j.ynstr.2020.100277. PMID: 33385020; PMCID: PMC7770962.