Probiotics For Moods and Stress


Probiotics For Moods and Stress

There are more bacteria in our gut than humans on the planet! 

Bacteria are everywhere and have key functions to our health!  They serve as the gatekeepers for things we want to enter and keep out of our bodies by helping digest foods, create vitamins, influence the function of other organs and our immune system.  70 – 80% of the immune system resides in the gut making the gut the largest immune organ in the body!

What do you do when you’re having an off day or you’re stressed to the max?

Eat ice cream? or are you a chips kind of person? maybe fries?

After reading this article, you may consider yogurt, a handful of walnuts, or maybe even some dark chocolate as your go-to mood-boosters and stress-busters.

Today, we’ll unpack some of the exciting (and preliminary) new research about the link between your gut health and moods/stress including: gut microbes (mostly bacteria), probiotic foods and supplements, and foods to feed those gut microbes and probiotics (aka “prebiotics”). 

Lots of buzz words out there like the genome, microbiome, and epigenetics which has led to new research and projects!

The Human Genome Project, The Human Microbiome Project

A genome is the complete map of an organisms genes and its DNA, kind of like a blueprint of how organisms are built and function.  The human microbiome is more of a study of the genes of the microbes in our body which may be as unique as a fingerprint.  So far they have discovered 20 million microbial genes.  They are learning that the microbes in our body also have the ability to send signals to turn on and off our human genes known as epigenetics.  By studying the genes of the microbes and learning how they turn signals on and off we hope to learn how we can avoid disease or promote optimal health.


They are the trillions of microbes that happily live in our gut. They help us by digesting foods, making vitamins, and even protecting us from the not-so-friendly microbes that may get in there.

Believe it or not, these friendly microbes have mood-boosting and stress-busting functions too!  They create neurotransmitters, like the ones in our brain, such as serotonin and GABA.  They create enzymes that can help us break down foods.  They also create essential building blocks in our bodies like vitamins, amino acids, short-chain fatty acids,

FUN FACT: There are more microbes inside our gut, than all of the human cells that make us. Yup, only 10% of our cells are human! The other 90% are microbes!  So, how can they NOT impact our health?  These microbial cells are collectively called the human microbiota.


The microbes that live in our guts are known as our “gut microbiota”.  But, just so you know, you also have microbiota communities on your skin, in your ears, nose, mouth and any other area exposed to the world.  Our gut microbiota is made up of all different kinds of microbes, bacteria, viruses, fungi, archaea, and protista – all small but mighty.

Fun fact:  the microbes in your gut weigh almost 5 pounds.

The microbes that we can ingest are known as “probiotics”.

“Probiotics” are live organisms that are beneficial to health that you can eat, drink, or take as a supplement. They’re what turn milk into yogurt, and cabbage into sauerkraut; and they are great for both your gut health and mental health.

Special probiotics that have mental health benefits are called “psychobiotics,” (psycho = mental health, and biotics = live). They’re live organisms that can benefit our psyche.

So, what’s the link between gut microbes, probiotics, and moods/stress?


Stress can alter the balance of microbes in our gut.

Several studies show that stressed rodents not only have increased stress hormones and stressed behaviors; but, they also have different gut microbes!

And this has been studied in people too.

One study showed that moms with high levels of stress hormones during pregnancy had infants with more of the “bad” gut microbes.

But, can it work the other way around? Can changing our gut microbes affect our moods and stress responses?

Studies of rodents that grow up without any gut microbes at all (in a “bacteria-free” environment) respond to stress more than mice with normal gut microbes. Then, when they’re given either a probiotic or gut microbes from non-stressed mice, their stress responses often go back to normal.


“Gut microbiota and probiotics alter behavior and brain neurochemistry.” (Ait-Belgnaoui, et. al., 2012)

That’s a pretty powerful statement!

Many animal studies show positive effects on behavior when they get probiotic supplements.

For example, after a probiotic, stressed rats had lower levels of both stress hormones and an inflammatory molecule associated with depression (“LPS” – lipopolysaccharide).

Human studies show that after a few weeks of taking probiotic foods or supplements, healthy people have reduced stress hormones, feelings of stress, negative thoughts, and sad moods. 

One fascinating study showed that when people took probiotics, brain MRI (magnetic resonance imaging) tests showed reduced brain activity for negative and aggressive thoughts!

So, as you can see, there is some concrete evidence on the positive effect that probiotics can have on moods and stress.

You might be wondering how exactly your gut can influence your moods…


It may not seem obvious or intuitive, but your body is interconnected in many ways.  The gut brain connection refers to the bidirectional communication between the brain and the gut.  The gut has its own nervous system known as the enteric nervous system which controls all muscle contractions and reflexes that happen during digestion.

Do you tell your gut to digest food?  Or does it work on its own?  The gut is considered to be the second brain.  It has more neurons than the brain and the spinal cord put together!  What?  The small intestine alone has roughly 100 million neurons.

What is a neuron?  It is  a nerve cell that communicates and transmits information throughout the body via neurotransmitters.  There are around 20-30 various neurotransmitters in the brain and in the gut making communication between the gut and the brain very efficient.

And more and more research is figuring out the “microbiota-gut-brain axis.” This axis is a very complex connection between your gut, its microbes, and your brain.

This new gut-brain connection has been named a “paradigm shift in neuroscience” (Dinan, 2017).

In fact, there are a number of ways that we’re beginning to understand how our gut microbes can affect our brain.

One is via the “vagus” nerve, which is a nerve that directly connects your gut to your brain. 

The other ways are through “biochemical messengers.” Biochemical messengers are made in your gut and travel through the body to communicate with other parts of the body, including your brain. Some examples of biochemicals are: cytokines which are molecules that mediate and regulate immunity, inflammation and hematopoiesis and tryptophan which is the amino acid that the neurotransmitters melatonin and serotonin are made from.

So, what can you do to nurture your own healthy gut microbes?


First, eat (and drink) probiotics. 

Probiotics can be eaten in yogurt, sauerkraut (and other fermented veggies), miso, tempeh, and kimchi. You can drink them in kefir or kombucha. Be sure to choose unpasteurized ones that will be refrigerated in your local grocer.

Of course, there are a number of probiotic supplements available too. The major probiotics available today include:  Lactobacillus, Bifidobacterium, soil based bacteria and spore forming bacteria.  Lactobacillus and Bifidobacterium both produce lactic acid.  Bacteria that produce lactic acid inhibit the growth of pathogens because they lower pH.  Lactic acid bacteria feed and nourish the gut lining and stimulate the immune system.  There are also soil based and spore forming bacteria.  Soil based bacteria are naturally found in the soil.  Spore formers have been around in nature for a long time.  When your gut is nutrient rich, these bacteria act like gardeners, they weed out the pesky bacteria and clean up the gut.

Look for probiotics that have at least 10 billion active cultures and multiple strains. I also suggest you look for one that has been “third party tested,” which means someone outside the company has tested it and says it’s a quality product.

So, those yummy gummy ones might not be the most effective. 

Oh, and always read the label before taking any supplements.
The probiotics with the most research are of the Bifidobacterium and Lactobacillus types.


PREbiotics are “compounds that, when fermented in the gut, produce specific changes in bacterial composition or activity”. They are your friendly gut microbes’ favorite delicacies so they’ll happily grow, and multiply. 

Prebiotics are basically foods that contain fibre. Things like fruits, vegetables, nuts, and seeds. Even dark chocolate (preferably with at least 70% cocoa).

Giving animals prebiotics can reduce stress hormones, and anxiety-related behaviors.

And in people, studies show that taking psychobiotics along with prebiotics can improve both the microbes in our gut, as well as our mood. 


The science behind interactions of gut microbes and mental health is still new and ongoing. Much of it is in rodents, with a few studies in people. Some show interesting links and promising potential to help with moods and other areas of mental and brain health.

More research, especially in humans, is needed; so I’ll be on the lookout for new studies in this young and promising area of mood-boosting and stress-busting nutrition.

Try eating more probiotics like in yogurt, kefir, miso, kimchi, and kombucha. Consider taking probiotic supplements (making sure you read the label and follow directions).

And don’t forget their favorite foods called prebiotics. Those are in fruits, vegetables, nuts and seeds (and even dark chocolate). 

Optimize your gut for more than just gut health, but mood-boosting and stress-busting too.

Bye bye blah moods, procrastination and low energy levels. Hello great grades, new exercise routines and feeling energetic throughout the entirety of the day.


Ait-Belgnaoui, A., Durand, H., Cartier, C., Chaumaz, G., Eutamene, H., Ferrier, L., Houdeau, E., Fioramonti, J., Bueno, L. & Theodorou, V. (2012). Prevention of gut leakiness by a probiotic treatment leads to attenuated HPA response to an acute psychological stress in rats. Psychoneuroendocrinology. 37(11):1885-95. doi: 10.1016/j.psyneuen.2012.03.024.


Bailey, M.T., Dowd, S.E., Galley, J.D., et al. (2011). Exposure to a social stressor alters the structure of the intestinal microbiota: implications for stressor-induced immunomodulation. Brain Behav Immun. 25(3):397–407.


Bharwani A, Mian MF, Foster JA, et al. (2016). Structural & functional consequences of chronic psychosocial stress on the microbiome & host. Psychoneuroendocrinology. 63:217–227.


Cryan, J.F. (2016). Stress and the Microbiota-Gut-Brain Axis: An Evolving Concept in Psychiatry. 

Can J Psychiatry. 61(4):201-3. doi: 10.1177/0706743716635538.


De Palma, G., Blennerhassett, P., Lu, J., Deng, Y., Park, A.J., Green, W., Denou, E., Silva, M.A., Santacruz, A., Sanz, Y., Surette, M.G., Verdu, E.F., Collins, S.M. & Bercik, P. (2015). Microbiota and host determinants of behavioural phenotype in maternally separated mice. Nat Commun. 2015 Jul 28;6:7735. doi: 10.1038/ncomms8735.


Dinan, T.G. & Cryan, J.F. (2016). Mood by microbe: towards clinical translation. Genome Med. 8(1):36. doi: 10.1186/s13073-016-0292-1.


Dinan TG1, Cryan JF. (2017). The Microbiome-Gut-Brain Axis in Health and Disease. Gastroenterol Clin North Am. 2017 Mar;46(1):77-89. doi: 10.1016/j.gtc.2016.09.007.


Kelly, J. R., Kennedy, P. J., Cryan, J. F., Dinan, T. G., Clarke, G., & Hyland, N. P. (2015). Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders. Frontiers in Cellular Neuroscience, 9, 392. 


Messaoudi, M., Lalonde, R., Violle, N., Javelot, H., Desor, D., Nejdi, A., Bisson, J.F., Rougeot, C., Pichelin, M., Cazaubiel, M. & Cazaubiel, J.M. (2011). Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects. Br J Nutr. 105(5):755-64. doi: 10.1017/S0007114510004319.


O’Mahony, S.M., Marchesi, J.R., Scully, P., et al. (2009). Early life stress alters behavior, immunity, and microbiota in rats: implications for irritable bowel syndrome and psychiatric illnesses. Biol Psychiatry. 65(3):263–267.


Rea, K., Dinan, T.G. & Cryan, J.F. (2016). The microbiome: A key regulator of stress and neuroinflammation. Neurobiol Stress. 4:23-33.


Rieder, R., Wisniewski, P.J., Alderman, B.L. & Campbell, S.C. (2017). Microbes and mental health: A review. Brain Behav Immun. 2017 Jan 25. pii: S0889-1591(17)30016-8. doi: 10.1016/j.bbi.2017.01.016.


Romijn, A.R. & Rucklidge, J.J. (2015). Systematic review of evidence to support the theory of psychobiotics. Nutr Rev. 73(10):675-93. doi: 10.1093/nutrit/nuv025.


Sarkar, A., Lehto, S.M., Harty, S., Dinan, T.G., Cryan, J.F. & Burnet, P.W. (2016). Psychobiotics and the Manipulation of Bacteria-Gut-Brain Signals. Trends Neurosci. 39(11):763-781. doi: 10.1016/j.tins.2016.09.002.


Sender, R., Fuchs, S. & Milo, R. (2016). Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biol 14(8): e1002533. doi:10.1371/journal.pbio.1002533


Sherwin, E., Sandhu, K.V., Dinan, T.G. & Cryan, J.F. (2016). May the Force Be With You: The Light and Dark Sides of the Microbiota-Gut-Brain Axis in Neuropsychiatry. CNS Drugs. 2016 Nov;30(11):1019-1041. doi: 10.1007/s40263-016-0370-3


Steenbergen, L., Sellaro, R., van Hemert, S., Bosch, J.A. & Colzato, L.S. (2015). A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood.

Brain Behav Immun. 48:258-64. doi: 10.1016/j.bbi.2015.04.003.


Zijlmans, M.A., Korpela, K., Riksen-Walraven, J.M., de Vos, W.M. & de Weerth, C. (2015).  Maternal prenatal stress is associated with the infant intestinal microbiota. Psychoneuroendocrinology. 2015 Mar;53:233-45. doi: 10.1016/j.psyneuen.2015.01.006.