Last updated January 27, 2022 by Lisa Richards, CNC

Can Probiotics Affect Your Mood?

Probiotics can affect your mood

In simple terms, probiotics are “healthy” bacteria, that when ingested can have a positive effect on health. They are particularly useful for maintaining a healthy composition of gut flora, and preventing or reversing conditions like Candida overgrowth. But new research is showing that they can also affect the way that we react to stressful situations.

The two most commonly discussed groups of probiotic microorganisms are lactic acid bacteria and bifidobacteria. (1) There are several specific species found in each group, and different strains are credited with different benefits. Many provide digestive benefits, including improving regularity, treating infectious diarrhea in infants and children, and treating Crohn’s disease and irritable bowel syndrome (IBS). We are starting to understand how they can also affect our emotions and reduce levels of stress and anxiety.

Can Probiotics Affect Your Mood?

Recent research suggests that there may be yet another area where probiotics could have positive health benefits – the brain. Scientists are currently investigating this possibility in several different ways. Some studies are being done to determine if gut bacteria communicate with the brain, how that communication occurs, and what, if any, effect these bacteria have. This is commonly known as the gut-brain axis. Separately, other researchers are looking into the connection between gut bacteria and our behavior and mood, while others are attempting to determine if probiotics hold any promise for treating specific mood disorders like depression.

Researchers from University College Cork in Ireland have made two important discoveries. (2) First, they determined that certain gut microbes communicate with the central nervous system (CNS). Second, they were able to show one way this communication takes place. In a study published by Proceedings of the National Academy of Sciences of the United States of America in 2011, these researchers sought to determine whether Lactobacillus rhamnosus, a lactic acid bacteria, would have an effect on a major CNS neurotransmitter, gamma-Aminobutyric acid (GABA), and whether the vagus nerve served as a mechanical pathway between the CNS and digestive tract.

The experiment involved feeding Lactobacillus rhamnosus to mice for 28 days, then carrying out a set of behavioral tests. GABA alterations are already associated with depression and anxiety. The researchers concluded that Lactobacillus rhamnosus affected GABA expression in various parts of the brain and xconsequently, “reduced stress-induced corticosterone and anxiety- and depression-related behavior.”  In order to evaluate the role of the vagus nerve the mice underwent vagotomy, or a surgical severing of the nerve. The researchers found that the mice who had undergone vagotomy did not demonstrate the same neurochemical and behavioral effects of the bacteria.

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In other words, mice that ingested the bacteria showed lower levels of anxiety, stress and depression but if these same mice had their vagus nerve severed, they did not show the lower levels. Researchers felt this established the vagus nerve as a communication pathway of the brain-gut axis, a mechanism whereby probiotic bacteria can indirectly affect our mood.

Probiotics And Behavioral Changes

In research published in a 2011 issue of the journal Gastroenterology, researchers from McMaster University in Hamilton, Ontario, studied the connections between intestinal flora and brain chemistry and behavior in mice. (3) They caused an imbalance of microbes (also called dysbiosis) in the digestive tracts of mice then administered behavioral evaluations. Their results showed, among other things, that replacing the bacteria of anxious mice with bacteria from fearless ones made the anxious mice more confident. Conversely, the bolder mice became less confident when their gut flora was replaced with that from anxious mice. These behavioral changes were attributed to changes in the central levels of Brain-Derived Neurotropic Factor in the mice.

Importantly, this research concluded that these changes were not caused by “the autonomic nervous system, gastrointestinal-specific neurotransmitters, or inflammation”, and ultimately could “contribute to psychiatric disorders in patients with bowel disorders.” In other words, people with digestive conditions that cause an imbalance in gut microbes might experience mood or behavior changes because of this imbalance.

If this is the case, then it might stand to reason that probiotics to correct these gut flora imbalances could treat or prevent the psychiatric disorders they might cause. Although more research needs to be done, these results are very interesting.

What Does The Future Hold?

Probiotics are well regarded for their ability to assist people maintain and improve their immune systems, digestive and uro-genital health. They are recommended both for healthy individuals, and for those who suffer from conditions like Candida Related Complex, diarrhea, IBS, yeast infections, or bacterial vaginosis. I also highly recommend that people taking antibiotics use probiotic supplements to restore the colonies if bacteria that are destroyed by their treatment.

If you’re looking for a high quality probiotic to restore healthy gut function and boost your immune system, I recommend the Balance ONE Probiotic.

Moving beyond the gut and exploring the effects of probiotics on the central nervous system and behavior is the future of probiotic research. Emerging evidence shows that specific intestinal flora can affect things like anxiety, stress and mood, and this could eventually lead to the development of alternatives to traditional pharmacological therapies.   The possibilities of probiotics for mental health are being eagerly investigated by scientists around the world.

References and Further Reading

  1. WebMD. “What are probiotics?”.
  2. Bravo et al, 2011. “Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve”.
  3. Bercik et al, 2011. “The Intestinal Microbiota Affect Central Levels of Brain-Derived Neurotropic Factor and Behavior in Mice”.
Filed under: Immune System, Probiotics
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  1. Jayne says:

    Hmm, interesting article!

    There’s one bit that puzzles me…

    The study in Ontario found that “replacing the bacteria of bold mice with bacteria from anxious ones made the bold mice calmer” …

    should this perhaps be “replacing the bacteria of bold mice with bacteria from anxious ones made the bold mice more anxious”?


    1. Great spot Jayne! I fixed that paragraph, thanks 🙂

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