5 min read

Many people ignore signs of an unhealthy digestive tract for far too long, often telling themselves that their symptoms are minor inconveniences. By failing to put their gut health first such as adding a probiotic supplement to their diet, they begin to feel the effects in their whole body. In truth, poor gut health can have a number of serious side effects including lowered immune system defenses, a slower metabolism, decreased energy levels--and even poorer mental health.

An increasingly large body of research conducted by leading universities around the world points to a strong connection between a person's gut microbiome and their propensity for developing and dealing with depression, anxiety and even post-traumatic stress disorder (PTSD).

The Connection Between Your Gut Health and Brain

It shouldn't come as too much of a surprise that our brains and our guts are strongly interconnected. After all, everyone has experienced the feeling of butterflies in their stomach when anxious or under stress, or has decided to follow a "gut feeling" when making an important decision.

To an increasing extent, however, researchers are finding that the digestive tract's bacterial ecosystem can have a direct and significant influence on how a person thinks and feels. The link between your gut health and your mood is complex, and scientists have differing theories on how the gut microbiome affects mood and emotional well-being.

Some researchers believe that the vast populations of beneficial microorganisms that populate our digestive tract play a direct role in producing emotion-regulating chemicals in our bodies, such as dopamine, serotonin, endorphins, and oxytocin; others have found that gut bacteria helps the body metabolize these substances, while still, other scientists have discovered that that microbes in the digestive tract can improve communication between the brain and the gut.

Whatever the exact connection, this link could signal a breakthrough for those Americans who face mental illness every year. For example, a 2010 study conducted by University College of Cork researchers found that the probiotic Bifidobacterium was as effective as a prescription antidepressant at reducing stress hormones and increasing perseverance in mice.

This incredible effect was reproduced in humans in a 2013 UCLA study: after eating normal probiotic-filled yogurt twice daily for four weeks, study participants had a significantly calmer response to emotionally-charged pictures than the control group did. With almost 60 million adults in the United States dealing with depression or anxiety in any given year, the potential to relieve symptoms or common mental illnesses by increasing probiotic intake is remarkable.

How the Bacteria of Your Gut Can Affect Your Anxiety Levels

Of course, you don't need to have been diagnosed with an anxiety disorder to benefit from the emotion-regulating effects of a healthy gut microbiome. Focusing on your digestive tract health can help you lower your everyday responses to anxiety-producing events. As Oxford University researchers have found, increasing your intake of prebiotics--a type of dietary fiber that is used as fuel by the good bacteria in your gut--can change the way your brain processes emotional information and lower your anxious response.

The Oxford study looked at a group of 45 adults in good health. Half of the study participants took a prebiotic supplement daily for three weeks; the other half was given a placebo. At the end of the study period, both groups were given computer tests designed to see how they processed emotionally-charged information, such as how they responded to positive and negative-sounding words.

Researchers found that the group who took the prebiotic focused more on the positive information than the negative as compared to those in the placebo group; this effect was noted to be similar to taking an antidepressant or anti-anxiety medication. Those in the group taking the prebiotic supplement also had reduced levels of the stress hormone cortisol in their saliva.

The Oxford University researchers were careful to point out that prebiotics and probiotics are not likely to be used as a therapy for anxiety and depression on their own. However, in conjunction with conventional treatments--or for those without these mental illnesses who still experience anxiety--supplements that help boost the health of the digestive tract have clearly been shown to help improve mental health as well.

The Role of Your Gut Microbiome in Your Body's Response to Traumatic Events

Even more incredibly, your gut health can influence your body and brain's response to extreme traumatic events. Characterized by changes in mood, intrusive thoughts and physical symptoms like difficulty concentrating and insomnia, post-traumatic stress disorder (PTSD) is a serious mental health condition that can be triggered after experiencing major trauma. However, not everyone who goes through such traumatic events develops PTSD, and one factor that researchers now believe may contribute to a person's likelihood of developing PTSD following trauma is their unique gut bacterial population.

Researchers at Stellenbosch University analyzed the gut microbiomes from study participants with PTSD alongside those of individuals who had experienced similar trauma but had not developed PTSD. These scientists found one significant difference between the two groups: those with PTSD had dramatically lower levels of three key bacterial strains--actinobacteria, lentisphaerae and verrucomicrobia--than those without PTSD. The exact role that these microbes play in determining PTSD susceptibility is still unclear, though researchers believe it may have to do with their role in immune system regulation and inflammation reduction.

In short, while the exact mechanisms by which the gut microbiome affects brain chemistry isn't entirely understood by scientists, it is clear that there's a strong connection between the two. Whether by directly producing neurotransmitters or helping the body metabolize these substances, a healthy bacterial population supported by probiotic supplements can help a person recover from certain mental illnesses or avoid them altogether--making it all the more important that every person takes steps to protect their gut health.


Desbonnet L, Garrett L, Clarke G, Kiely B, Cryan JF, Dinan TG. Effects of the probiotic Bifidobacterium infantis in the maternal separation model of depression. Neuroscience. 170(4):1179-88. 2010.

Tillisch K, Labus J, Kilpatrick L, Jiang Z, Stains J, Ebrat B, Guyonnet D, Legrain-Raspaud S, Trotin B, Naliboff B, Mayer E. Consumption of Fermented Milk Product With Probiotic Modulates Brain Activity. Gastroenterology. 144(7): 10.1053. 2013.

Schmidt K, Cowen P, Harmer C, Tzortzis G, Errington S, Burnet P. Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers. Psychopharmacology. 232(10): 1793-1801. 2015.

Hemmings S, Malan-Müller S, van den Heuvel L, Demmitt B, Stanislawski M, Smith D, Bohr A, Stamper C, Hyde E, Morton J, Marotz C, Siebler P, Braspenning M, van Criekinge W, Hoisington A, Brenner L, Postolache T, McQueen M, Krauter K, Knight R, Seedat S, Lowry C. The Microbiome in Posttraumatic Stress Disorder and Trauma-Exposed Controls. Psychosomatic Medicine. 79 (8): 936. 2017