Microbiome and Mood: How Does Our Gut Affect How We Feel?

June 03, 2022 8 min read

Microbiome and Mood: How Does Our Gut Affect How We Feel? | Layer Origin Nutrition

Microbes, Mood, and Mental Health: How Do Our Gut Bacteria Affect How We Feel?

If you’ve ever gotten a stomachache before an important presentation, had a low appetite after receiving stressful news, or felt the fluttering of butterflies during a first date, you’ve experienced firsthand the relationship between your gut and your mind. 

While we know that the collection of bacteria, fungi, and other microbes in our gastrointestinal tracts make up the gut microbiome, you may be less familiar with the ‘psychobiome.’ This recently coined term describes how our gut microbes affect the ways we think, feel, and act.

The link between microbes and the mind has been acknowledged for centuries, with the ancient Greeks believing mental disorders came from the digestive tract producing too much “black bile.” Although we’ve come a long way since then, researchers are still uncovering the myriad ways that the health of our guts also affects the health of our mind, mood, and mental status.

The Gut-Brain Axis: Is the Gut Our “Second Brain”?

The intricate crosstalk between the gut and the brain plays a vital role in both gastrointestinal function and several aspects of mental and cognitive health. Referred to as thegut-brain axis, these two organs have a bi-directional relationship and are constantly in communication — so much so that the gut has been dubbed our “second brain.” 

Evidence of this can be seen in people with digestive disorders. For example, many patients with irritable bowel syndrome (IBS) also experience depression or anxiety, and stress often exacerbates symptomatic flares of inflammatory bowel disease (IBD). 

There are several routes by which intestinal microbes can act on the brain: 

  1. Gut microbes cause newly discovered sensory cells in the gut called neuropod cells to stimulate the vagus nerve. (The “pod” in neuropod comes from their foot-like projection that extends outward to form a synapse-like connection with nerve cells, including the vagus nerve.) The vagus nerve leads a direct connection to the brain and is a central component of the gut-brain axis, as it runs from the base of the brain to the abdominal organs. 
  2. A second route is through messenger molecules, which get secreted by gut microbes and can permeate blood vessels and travel directly to the brain. 
  3. In an indirect route, gut bacteria trigger enteroendocrine cells to send signals throughout the body. Enteroendocrine cells live in the gut lining, releasing hormones and compounds that regulate digestion and insulin secretion. They also promote the release of serotonin — our “happy” neurotransmitter — from the gut into the rest of the body, influencing brain health and mood. 
  4. Lastly, gut bacteria indirectly modulate immune cells and inflammatory pathways that affect the brain. Recent research has linked increased inflammation to brain-related disorders, including autism and depression. 

     Recent Research on the Microbiome, Mood, and Mental Health

    Although scientists have known about the gut-brain relationship for decades, it has only been over the past few years that research on the role of gut microbes on mental health disorders has exploded. 

    From mood and memory to behavior and brain cells, researchers are now uncovering much more about the psychobiome — and how specific bacteria may soon be used as treatments to help us feel better.  Let’s take a closer look at how the microbiome affects four common mental health concerns: depression, bipolar disorder, anxiety, and stress.

    1. Major Depressive Disorder

    Major depressive disorder (MDD), or clinical depression, is a highly prevalent mental health condition, affecting over10% of the global population

    It’s thought that gut microbiome disturbances play a role in depression in several ways. These include impacting the release of the “feel-good” neurotransmitters serotonin and dopamine, causing an abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis and triggering pro-inflammatory responses. 

    In asystematic review of 24 observational and experimental studies, researchers found significant differences between the gut microbiomes of people with MDD and healthy controls. Those with MDD exhibited lower bacterial diversity and changes in the abundance of specific bacteria. In experimental studies, probiotic and synbiotic (prebiotic plus probiotic) treatment modestly improved patients’ depressive symptoms. 

    A2016 randomized controlled trial looked at the effects of supplemental probiotics on people with MDD. Forty adults with MDD were randomized to take either a probiotic capsule containingLactobacillus acidophilus,Lactobacillus casei, and Bifidobacterium bifidum or a placebo. After eight weeks, those in the probiotic group exhibited significantly decreased (i.e., improved) scores on a depression scale and dampened markers of inflammation and metabolic dysfunction. 

    2. Bipolar Disorder

    Bipolar disorder is another common mental condition, causing mood swings with manic or hypomanic “highs” and depressive “lows.” However, despite its prevalence, the available research on the microbiome and bipolar disorder is still in its infancy. 

    Evans et al. (2017) first studied gut microbiome differences in people with bipolar disorder, finding that they had markedly reduced levels of the bacteriaFaecalibacteriumand a bacteria in theFirmicutes phylum.Other research has found bipolar disorder patients to harbor higher levels ofActinobacteria

    One clinical trial has looked at the effects of supplemental probiotics on 38 hospitalized patients with bipolar disorder. Those taking a mixed probiotic (Bifidobacterium bifidum, Bifidobacterium lactis, Bifidobacterium langum,and Lactobacillus acidophilus) for eight weeks experienced significant improvements on tests assessing manic and depressive symptoms compared to their baseline levels. However, the results were not significantly different from the control group, suggesting a placebo effect. 

    3. Generalized Anxiety Disorder

    Anxiety disorders are the most common mental health condition, with18% of the American adult population being diagnosed with anxiety — and probably many more who have never sought treatment. Anxiety and depression are closely linked, with almost one-half of people with depression also suffering from anxiety. 

    In a recent study, researchers monitored gut microbiota changes in people with anxiety. Compared to healthy controls, people with anxiety exhibited decreased bacterial diversity in their gut microbiomes with overgrowths of some unhealthy bacteria, likeStreptococcus

    Further, after the anxious patients underwent Mindfulness-Based Cognitive Therapy, they had reduced anxiety symptoms, and their gut microbiota resembled those of the healthy controls. Future research should assess whether combining behavioral therapy and probiotics works synergistically to suppress anxiety.

    4. Acute and Chronic Stress

    Chronic stress has been shown to impact the intestinal barrier, leading to increased gut permeability and inflammation. Often referred to as “leaky gut,”increased barrier permeability is linked to mental health conditions, including major depressive disorder. 

    Stress also impacts the HPA axis — the physiological system that mediates all stress responses by modulating the release of hormones like cortisol, our primary stress hormone. The HPA axis is highly involved in the gut-brain crosstalk, and dysregulation of the HPA axis is known to play a role in the development of mental health disorders. 

    Some studies have looked at the effects of probiotics on acute stress.One trial subjected people to complicated mental math challenges in front of an audience combined with social threat components. (Imagine Gordon Ramsey watching and evaluating you while you publicly work on difficult math challenges — essentially, it’s designed to make you very stressed out.) 

    In healthy people who underwent this stress test, those taking probiotic supplements for four weeks prior had subtly altered brain activity in regions known to regulate emotion and stress responses. 

    Similar results were seen in ananimal study looking at chronic stress. Rats subjected to eight weeks of chronic mild stress were randomized to take either a probiotic supplement or a placebo. 

    The probiotic-supplemented rats displayed significantly less anxiety and stress during behavioral and exploratory maze tests that were designed to assess stress. The probiotics also improved specific brain metabolites, suggesting that probiotics may stabilize stress-related neuro-metabolites to prevent stress and anxiety. 

    Key Takeaway

    The constant communication between our guts and brains plays a role in the development of mental health disorders, including depression, anxiety, stress, and bipolar disorder. Studies on the gut-brain axis — and how to improve the function of both — are ever-growing, hopefully leading to potential clinical implications in the future. This connection is not just for people with poor mental health — probiotics may also maintain or enhance mood and reduce stress in healthy people.  

    As we learn more about which bacteria are reduced or elevated in people with specific mental health concerns, therapeutics may be able to be tailored to improve their symptoms. Although more research is needed, the available evidence suggests that modulating the gut microbiome via probiotics may help maintain or improve mental health and mood. 

    For now, as we don’t know for sure which bacterial strains are best for promoting healthy and stable moods, supporting your gut microbiome in other ways is never a bad idea. For example, increasing your consumption of fermented foods, like sauerkraut, yogurt, kefir, kimchi, and pickles, and boosting your prebiotic fiber intake are good places to start to benefit your gut and its trillions of bacteria. 

     

    Written By: 

    Cambria Glosz, MS, RD

     

    References:

    Akkasheh G, Kashani-Poor Z, Tajabadi-Ebrahimi M, et al. Clinical and metabolic response to probiotic administration in patients with major depressive disorder: A randomized, double-blind, placebo-controlled trial.Nutrition. 2016;32(3):315-320. doi:10.1016/j.nut.2015.09.003

    Alli SR, Gorbovskaya I, Liu JCW, Kolla NJ, Brown L, Müller DJ. The Gut Microbiome in Depression and Potential Benefit of Prebiotics, Probiotics, and Synbiotics: A Systematic Review of Clinical Trials and Observational Studies.Int J Mol Sci. 2022;23(9):4494. Published 2022 Apr 19. doi:10.3390/ijms23094494

    Banerjee A, Sarkhel S, Sarkar R, Dhali GK. Anxiety and Depression in Irritable Bowel Syndrome.Indian J Psychol Med. 2017;39(6):741-745. doi:10.4103/IJPSYM.IJPSYM_46_17 

    Breit S, Kupferberg A, Rogler G, Hasler G. Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders. Front Psychiatry. 2018;9:44. Published 2018 Mar 13. doi:10.3389/fpsyt.2018.00044

    Carabotti M, Scirocco A, Maselli MA, Severi C. The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems.Ann Gastroenterol. 2015;28(2):203-209.PMID:25830558

    Chudzik A, Słowik T, Kochalska K, et al. Continuous Ingestion of Lacticaseibacillus rhamnosus JB-1 during Chronic Stress Ensures Neurometabolic and Behavioural Stability in Rats. Int J Mol Sci.2022;23(9):5173. Published 2022 May 5. doi:10.3390/ijms23095173

    Edebol Carlman HMT, Rode J, König J, et al. Probiotic Mixture Containing Lactobacillus helveticus, Bifidobacterium longum and Lactiplantibacillus plantarum Affects Brain Responses to an Arithmetic Stress Task in Healthy Subjects: A Randomised Clinical Trial and Proof-of-Concept Study.Nutrients. 2022;14(7):1329. Published 2022 Mar 22. doi:10.3390/nu14071329

    Eslami Shahrbabaki M, Sabouri S, Sabahi A, et al. The Efficacy of Probiotics for Treatment of Bipolar Disorder-Type 1: A Randomized, Double-Blind, Placebo-Controlled Trial.Iran J Psychiatry.2020;15(1):10-16.

    Evans SJ, Bassis CM, Hein R, et al. The gut microbiome composition associates with bipolar disorder and illness severity.J Psychiatr Res. 2017;87:23-29. doi:10.1016/j.jpsychires.2016.12.007

    Huang TT, Lai JB, Du YL, Xu Y, Ruan LM, Hu SH. Current Understanding of Gut Microbiota in Mood Disorders: An Update of Human Studies.Front Genet.2019;10:98. Published 2019 Feb 19. doi:10.3389/fgene.2019.00098

    Kaelberer MM, Rupprecht LE, Liu WW, Weng P, Bohórquez DV. Neuropod Cells: The Emerging Biology of Gut-Brain Sensory Transduction.Annu Rev Neurosci.2020;43:337-353. doi:10.1146/annurev-neuro-091619-022657

    Kelly JR, Kennedy PJ, Cryan JF, Dinan TG, Clarke G, Hyland NP. Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders.Front Cell Neurosci. 2015;9:392. Published 2015 Oct 14. doi:10.3389/fncel.2015.00392

    Lee CH, Giuliani F. The Role of Inflammation in Depression and Fatigue. Front Immunol.2019;10:1696. Published 2019 Jul 19. doi:10.3389/fimmu.2019.01696

    Lim GY, Tam WW, Lu Y, Ho CS, Zhang MW, Ho RC. Prevalence of Depression in the Community from 30 Countries between 1994 and 2014.Sci Rep.2018;8(1):2861. Published 2018 Feb 12. doi:10.1038/s41598-018-21243-x

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    Wang Z, Liu S, Xu X, et al. Gut Microbiota Associated With Effectiveness And Responsiveness to Mindfulness-Based Cognitive Therapy in Improving Trait Anxiety.Front Cell Infect Microbiol. 2022;12:719829. Published 2022 Feb 24. doi:10.3389/fcimb.2022.719829


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