What’s Your “Gut Feeling”? How Bacteria in Your Gut Can Affect Your Mood


The human brain is a fascinating organ made up of billions of neurons continuously firing electrical signals that influence what we do, think, and feel. However, many people do not realize that the human body also has a “second brain!” This second brain, located in the gut, is often overlooked but equally important in regulating our thoughts and emotions. In fact, a growing body of research indicates that the health of the gut and its resident microbes have a profound effect on mental health. Research also indicates factors that disrupt the gut microbiome may contribute to mental health disorders such as depression and anxiety. Learn more about how the gut microbiome is tied to mental health, and more importantly, what you can do to optimize the health of your gut microbiome to boost your mood and mental health.

The brain and the gut are closely linked
Mental illness is quite common in the United States. Current statistics indicate that one in six American adults has a mental illness such as depression or anxiety. (1) The conventional medical approach to treating mental health disorders is heavily focused on medication and views the brain as an entity distinct from the rest of the body. However, an emerging body of evidence demonstrates that the function of the brain is intrinsically linked to the health of the gut and that mental health problems may, in fact, stem from imbalances in the gut microbiome.(2)

In animal studies, mice with lower levels of beneficial Lactobacilli have been found to be less resilient in stressful situations and more prone to depression. (3) In humans, it has been found that depressed patients have significantly altered gut microbiomes compared to healthy controls, with a preponderance of pathogenic bacteria and lower levels of beneficial bacteria. (4) Patients with bipolar disorder and obsessive-compulsive disorder also demonstrate significant alterations in their gut microbiomes which may adversely impact mental health. (5)(6) This research suggests that the balance of bacteria in the gut significantly impacts mental function.

How do gut bacteria influence mental health?
The human gut contains trillions of bacteria and a special set of nerve cells called the enteric nervous system. Together, the microbes and nerves comprise the body’s “second brain.” There are two potential mechanisms by which gut bacteria interact with the enteric nervous system, thereby influencing the function of the “second brain” and mental health:

Pathogenic gut bacteria, which predominate when the microbiome is imbalanced, produce metabolites that promote an inflammatory immune response and increase the activity of the sympathetic nervous system. The sympathetic nervous system is the branch of the central nervous system responsible for the “fight or flight” response. (7) Activation of this response produces anxiety. Conversely, beneficial gut bacteria, such as Lactobacilli and Bifidobacteria, produce compounds that suppress inflammation and the sympathetic nervous system reaction.

Certain gut bacteria produce neurotransmitters, such as serotonin, that communicate with the brain via the vagus nerve, which connects the enteric nervous system of the gut to the brain. Bacterial imbalances in the gut may alter neurotransmitter levels and disrupt mental health. (8)

Strategies for balancing the microbiome and improving mental health
To improve mental health, it is crucial that we establish a healthy gut microbiome. Here are some strategies for balancing your gut microbiome and promoting optimal mental health.

Eat a whole foods nutrient-dense diet
Studies show that traditional, whole foods are superior for mental health. (9) One of the reasons why a whole foods diet may benefit mental health is because this type of diet contains a special type of fiber, prebiotic fiber, that feeds beneficial gut bacteria. Prebiotic fiber is found in foods such as asparagus, garlic, onions, leeks, apples, and legumes. Consuming fermented foods such as sauerkraut and kimchi may also benefit mood by supplying the gut with live, probiotic bacteria. When gut bacteria are well-fed and happy, they help create a happy, healthy you!

Try a probiotic supplement
Research indicates that probiotics may act as natural antidepressants by producing metabolites that suppress inflammation and the sympathetic nervous system response. In animal models of psychological stress, supplementation with Bifidobacterium infantis, Lactobacillus helveticus, and Lactobacillus rhamnosus has been found to reduce anxiety and depressive behaviors. (10)(11)(12) Several human trials have also found a significant benefit of probiotic supplementation on parameters of mental health. In one study, supplementation with a multispecies probiotic containing Lactobacilli and Bifidobacteria reduced self-reported sad mood and negative thoughts in adults. (13) In another human study, supplementation with Bifidobacterium longum led to reduced stress and improved memory. (14) These findings suggest that taking a multispecies probiotic containing Lactobacilli and Bifidobacteria may be one way to significantly improve mental health!

Limit antibiotic use
Disruption to the gut microbiome by antibiotics may induce cognitive impairment and poor mental health by disturbing the balance of beneficial and pathogenic bacteria and the neuroactive substance they produce. (15) To promote optimal mental health, it is best to be judicious with antibiotic use and only use them when necessary.

Reduce stress
Psychological stress perpetuates a vicious cycle of poor mental health by lowering levels of beneficial bacteria in the gut that reduce inflammation and modulate the stress response. Stress-reduction practices such as yoga and meditation may benefit mental health by helping you maintain a balanced, gut microbiome.

Final thoughts
If you or someone you love has experienced depression, anxiety, or other mental health issues, know that it is not “all in your head;” in fact, much of the problem may lie in your gut! However, there is hope! By restoring balance to the gut microbiome using a whole foods diet, probiotics, and stress reduction techniques, it may be possible to improve your mood and create optimal mental health that lasts a lifetime.


  1. Mental Illness. National Institute of Mental Health. https://www.nimh.nih.gov/health/statistics/mental-illness.shtml. Updated November 2017. Accessed January 17, 2018.
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  6. Rees JC. Obsessive–compulsive disorder and gut microbiota dysregulation. Med Hypotheses. 2014; 82(2): 163-166. https://www.sciencedirect.com/science/article/pii/S0306987713005550. Accessed January 17, 2018.
  7. Bailey MT, Dowd SE, Galley JD, et al. Exposure to a social stressor alters the structure of the intestinal microbiota: implications for stressor-induced immunomodulation. Brain Behav Immun. 2011; 25(3): 397-407. https://www.ncbi.nlm.nih.gov/pubmed/21040780. Accessed January 17, 2018.
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  9. Rahe C, Unrath M, Berger K. Dietary patterns and the risk of depression in adults: a systematic review of observational studies. Eur J Nutr. 2014; 53(4): 997-1013. https://www.ncbi.nlm.nih.gov/pubmed/24468939. Accessed January 17, 2018.
  10. Desbonnet L, Garrett L, Clarke G, et al. Effects of the probiotic Bifidobacterium infantis in the maternal separation model of depression. Neuroscience. 2010; 170(4): 1179-1188. https://www.ncbi.nlm.nih.gov/pubmed/20696216. Accessed January 17, 2018.
  11. Ohland CL, Kish L, Bell H, et al. Effects of Lactobacillus helveticus on murine behavior are dependent on diet and genotype and correlate with alterations in the gut microbiome. Psychoneuroendocrinology. 2013; 38(9): 1738-1747. https://www.ncbi.nlm.nih.gov/pubmed/23566632. Accessed January 17, 2018.
  12. Bravo JA, Forsythe P, Chew MV, et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci USA. 2011; 108(38): 16050-16055. https://www.ncbi.nlm.nih.gov/pubmed/21876150. Accessed January 17, 2018.
  13. Steenbergen L, Sellaro R, van Hemert S, et al. A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. Brain Behav Immun. 2015; 48: 258-264. https://www.ncbi.nlm.nih.gov/pubmed/25862297. Accessed January 17, 2018.
  14. Allen AP, Hutch W, Borre YE, et al. Bifidobacterium longum 1714 as a translational psychobiotic: modulation of stress, electrophysiology and neurocognition in healthy volunteers. Transl Psychiatry. 2016; 6(11): e939. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314114/#!po=2.17391. Accessed January 17, 2018.
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