• Allison Williams, ND

A Healthy Gut Equals a Happy Mind

The saying “you are what you eat” was right. Moreover, you are what you eat, and you are what you eat ‘eats’ and the metabolites they produce. You have bacteria that live in your intestines that digest the food that you eat. You are breaking food down into carbohydrates, proteins, and fats for yourself but also for them. I jokingly refer to them as “bacterial pets” to my patients, although, I think it’s more truthful than anything else.

You see, each and every one of us is a superorganism. We are the trillions of cells that compose ‘ourselves’ but we are also the trillions of microbes that live within us too1. It’s truly remarkable to be alive and to be a composite of so much individual life working together in a balance (or imbalance) of hormones, chemical messengers, and neurotransmitters that directly influence our thought and emotion.

Now, all of that being said, if our ‘bacterial pets’ are unhappy, then we are unhappy in a sense. The health of the gastrointestinal system is contingent on many factors from optimal levels of “good” bacteria, integrity of the GI wall, adequate fiber, ideal production of short-chain fatty acids, and also influenced by your own hormone production. All of these aspects of gastrointestinal health and their subsequent relationship to mood describes the gut-brain axis, which is a growing field of scientific study.

The Gut-Brain Connection

In a review by Severence et al. they delved into the gut-brain axis as it relates to different biomarkers related to neuropsychiatry3. They brought up a cogent point about most psychiatric conditions being devoid of of “biochemical evidence of measurable physiologic pathology”. Which basically means, we can’t run a lab test and say ‘this lab tests suggests you have depression or anxiety or a bipolar condition like we would in diabetes or hypothyroidism’ . However, they later delved into different biomarkers associated with metabolic dysfunction, systemic inflammation, and bacterial imbalances related to schizophrenia and major depressive disorder. Furthermore they discussed that bio-markers of systemic inflammation, like high sensitivity CRP (hs-CRP) are commonly associated with psychiatric patients versus controls.

What does all of this mean? That within our gut are bacteria that if not optimal can contributed to negatively impacting our mental health. It would be safe to extrapolate that anyone with an imbalanced gastrointestinal flora may be impacted (in varying degrees). Our gut talks to our brain, and our brain talks to our gut. Remember, we are a superorganism. Everything in us is connected.

We need “good” bacteria in our gut

In one study on mice assessing early colonization of GI microbiota it was suggested that early colonization directly impacts genes that influence the neuronal pathways that lead to nervous system development and anxiety4. What lives in the GI tract directly impacts gene expression and nervous system function!

There is a plethora of research on Lactobacillus and anxiety which should be one of the predominant bacteria in a healthy GI tract. While there are numerous rat studies touting its efficacy in reducing stress hormone release and nervousness, Chong et al did a study on Lactobacillus plantarum DR7 in humans showing it improved biomarkers associated with cognition, mental health, and memory5. Yes, bacteria improving brain function. So cool!

Bacterial Diversity is where it’s at

Bacterial diversity is paramount to a healthy gastrointestinal microbiome. Not only do we need lots of different ‘bacterial pets’, and the ‘right kind of pets’, but we need a lot of different species.

Jiang et al. did a comprehensive study on people diagnosed with Major Depressive Disorder and found their biodiversity significantly differed from subjects without MDD6. Subjects with MDD were found to have decreased levels of Lachnospiraceae and Ruminococcaceae which are associated with the ability to breakdown carbohydrates into short-chain fatty acids (SCFA). SCFAs are integral in maintaining good gut integrity, thus, lower levels of these bacteria could contribute to thinning of the GI lining. Additionally subjects with MDD were found to have overgrowth of bacteria known to be inflammogenic. Their study covers the disparity in GI microbiota in greater depth than discussed here, but in summation, it evidences that the bacteria living in our gut can influence our mental health and can be correlated with depression.

Putting it all together

There is so much more to be said about the gut-brain axis but my goal in this article was to introduce you to the idea that there is more to your mind than just the abstract conceptualization of your thoughts. The development of a thought or feeling is a complex composite of our physiology as well. And, we must consider how our thoughts and emotions are very much impacted by our gastrointestinal health. This is in turn influenced by our diets, exposure to stress, the bacteria that live within our guts, exercise, and even different environmental factors.

Be mindful of your gut. Lingering digestive issues, antibiotic use, chronic stress, poor nutrition, etc can all be signals you need to take better care of your gut because a healthy gut leads to a happier mind.

*Please note that this discussion focuses on the gastrointestinal microbiome, but you have bacteria everywhere in your body. Your nasal passages, respiratory system, skin, etc that all ‘talk to each other’ through something called quorum sensing. We are so very amazingly complex.

Note: The information on this blogpost is provided for informational purposes only and not intended to replace diagnosis and treatment by a qualified health care practitioner. Consult your medical care provider before making any changes to your diet, lifestyle, or healthcare plan.


  1. Sender R, Fuchs S, Milo R. Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biol. 2016;14(8):e1002533. Published 2016 Aug 19. doi:10.1371/journal.pbio.1002533

  2. Jones MP, Dilley JB, Drossman D, Crowell MD. Brain-gut connections in functional GI disorders: anatomic and physiologic relationships. Neurogastroenterol Motil. 2006;18(2):91-103. doi:10.1111/j.1365-2982.2005.00730.x

  3. Emily G. Severance, Robert H. Yolken. Tracking a dysregulated gut-brain axis with biomarkers of the microbiome. Biomarkers in Neuropsychiatry. 2020;2(100009-). doi:10.1016/j.bionps.2019.100009

  4. S.M. Collins, M. Surette, P. Bercik, The interplay between the intestinal microbiota and the brain, Nat. Rev. Microbiol. 10 (2012) 735–742.

  5. Chong HX, Yusoff NAA, Hor YY, et al. Lactobacillus plantarum DR7 alleviates stress and anxiety in adults: a randomised, double-blind, placebo-controlled study. Benef Microbes. 2019;10(4):355-373. doi:10.3920/BM2018.0135

  6. Jiang H, Ling Z, Zhang Y, et al. Altered fecal microbiota composition in patients with major depressive disorder. Brain Behav Immun. 2015;48:186-194. doi:10.1016/j.bbi.2015.03.016


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