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Does Your Gut Shape Your Mood?

by , | Last updated Mar 12, 2026 | Brain Health, Mental Health, Mood

The myriads of bacteria in the gut help the body digest food and stimulate the immune system, and they also impact your mood. Seriously, your intestines host 2000 different known species of bacteria.  Each person has a different proportion of bacterial species and strains in his or her gut.

The Gut-Brain Axis

The gut-brain axis is a bidirectional communication network between the intestines to the central nervous system and includes the network that links the central nervous system to the enteric nervous system that supplies the gut. This network also includes the endocrine, the immune, and the metabolic connections.1  Additionally, the autonomic nervous system, hypothalamic-pituitary-adrenal axis, and nerves within the gastrointestinal (GI) tract, all link the gut and the brain.2 Simply put, the brain “talks” to the gut, and conversely the gut communicates to brain, and consequently affects cognition and mood. Now, the gut microbiome is increasingly recognized as a major influencer of central nervous system function through the gut–brain axis.3

Gut Microbes and Brain Development

Research now shows that normal adult brain function depends on the presence of gut microbes during development.4  Studies suggest the composition of the microbiota has the potential to either decrease or increase the activity of hippocampal brain-derived neurotrophic factor (BDNF), an important protein involved in neuronal plasticity and cognition. The ability to reorganize itself by forming new neural connections and pruning unused ones. BDNF acts as a fertilizer for synapses in the brain. The microflora in your intestines substantially and extensively influences the gut-brain relationship and, consequently, cognition, decision making, mood regulations, emotions, the function of the adrenal glands, and even neuromuscular health!1  3

Gut Bacteria Affects the Brain

Your gut bacteria help to determine how many new brain cells you produce; how permeable your brain is to toxic substances; and how well-nourished and protected your brain cells are.5   Gut dysbosis (unfriendly bacteria predominates over beneficial bacteria) or decreased diversity in gut bacteria significally contributes to ow-grade systemic inflammation, impaired ability of the brain to wire itself and undesirable responses to stress.3

Anxiety, depression, and autism spectrum disorders now have well-established links to functional GI disruptions. Gut dysbiosis reduces tryptophan availability and serotonin synthesis.6 Serotonin is a neurotransmitter that enables us to have a positive outlook. Irritable bowel syndrome can have a psychological component associated with gut dysbiosis in which harmful bacteria outnumber beneficial bacteria.7 

Some strains of intestinal bacteria manufacture compounds that have positive effects on the nervous system, while other species of bacteria produce byproducts that exert detrimental effects on the brain and your mood. There have been a few trials where patients with depression have been given probiotic treatments and responded favorably. No doubt about it: gut bacteria seriously affect mood and influence behavior. 8 1

Stressed? Could Be Your Gut Bacteria!

Bienenstock and Forsythe used a “social defeat” scenario in which smaller mice were exposed to larger, more aggressive ones for a couple of minutes daily for 10 consecutive days. The smaller mice showed signs of heightened anxiety and stress–nervous shaking, diminished appetite, and less social interaction with other mice. The researchers then collected fecal samples from the stressed mice and compared them to those from calm mice. There was an imbalance in the gut microbiota of the stressed mice. The gut and bowels have a very complex ecology. Unfortunately, the less diversity there was, the greater the disruption to the body.

These scientists then fed live bacteria (probiotics) from the calm rodents to the stressed mice.  They were actually able to control the moods of the anxious mice by feeding them healthy microbes from fecal material collected from the calm mice. Using MRI technology, they also noted favorable changes in brain chemistry.  Interestingly enough, not only did the behavior of the mice substantially improve with the probiotic treatment, but it also continued to get better for several weeks afterward. The MRI technology enabled the scientists to see certain chemical biomarkers in the brain when the mice were stressed and when they were taking the probiotics. 9

Nerve Attack and Depression: The Gut Connection

The thinning of myelin (nerve insulation) is seen in such conditions as multiple sclerosis, depression, and social isolation. Myelin is the insulating sheath surrounding the axons of many nerve cells that allows for faster electrical impulse conduction. Without healthy myelin, nerve impulses from one nerve cell to another are significantly slowed. Rodent studies found that bacteria from the gut produce metabolites that can affect the myelin content in the brains of mice and induce depression-like symptoms.10

In one remarkable experiment, scientists relocated fecal bacteria from the gut of depressed mice to genetically distinct mice that did not manifest any signs of depression. What happened? The study showed that the transfer of microbiota was sufficient to induce social withdrawal behaviors and even change the activity of myelin genes and myelin content in the brains of the recipient mice. In other words, bacteria in your gut produce metabolites that have the capacity to affect the myelin content and your mental health, irrespective of genetics.11

Help for Depression

Dietary fibers, primarily soluble fibers, provide the gut microbiota’s primary energy source. Short-chain fatty acids (SCFAs), especially butyrate, promote synaptic plasticity, reduce the brain’s permeability to toxins, support attention/executive performance, and memory.12 Resistant starch found in foods like legumes and cooked and cooled potoes and cooked and cooled whole grains h shown to i butyrate production.13  The anthocyanins in blueberries have been shown to increase the abundance of Akkermansia muciniphila, a bacterium linked to improved mental and metabolic health and reduced markers of systemic inflammation.14 ((13 Minimal processed berries are superior.

Can Probiotics Help?

In a randomized, double-blind study, administration of a combination of L acidophilus, L casei, and Bifidobacterium bifidum was given to participants who were clinically depressed. After 8 weeks of intervention, patients who had major depression and who received probiotic supplements experienced significantly fewer signs and symptoms associated with depression. Once more, they had a lower inflammatory marker, known as hsC-reactive protein. This is important because depression fuels inflammation in the brain, and the converse is also true. 15  A systematic review of ten clinical trials found that most of the studies found positive results on measures of depressive symptoms.16 More studies are warranted to determine which gut microbes help depression

I am not saying that every case of depression is caused by an imbalance between the good and harmful gut bacteria, or can be treated successfully by probiotics. Other causes of depression such as harmful lifestyle practices, cognitive distortions, relationship problems, and spiritual issues need to be addressed. Gut bacteria, however, should not be overlooked in the treatment of this condition. Why? Emerging data reveals that there is communication between the gut and the brain in anxiety, depression, cognition, and autism spectrum disorder.17 Click this link for how to improve you gut microbiome.

  1. Appleton J. The Gut-Brain Axis: Influence of Microbiota on Mood and Mental Health. Integr Med (Encinitas). 2018 Aug;17(4):28-32. https://pmc.ncbi.nlm.nih.gov/articles/PMC6469458/[↩][↩][↩]
  2. Appleton J., The Gut-Brain Axis: Influence of Microbiota on Mood and Mental Health. Integr Med (Encinitas) 2018 Aug; 17(4): 28–32.[↩]
  3. Diotaiuti P, et al., The Gut Microbiome and Its Impact on Mood and Decision-Making: A Mechanistic and Therapeutic Review. Nutrients. 2025 Oct 24;17(21):3350.  https://pmc.ncbi.nlm.nih.gov/articles/PMC12609437/[↩][↩][↩]
  4. California Institute of Technology. “Microbes help produce serotonin in gut.” ScienceDaily. ScienceDaily, 9 April 2015. www.sciencedaily.com/releases/2015/04/150409143045.htm[↩]
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  10. Alimentary Pharmabiotic Centre – University College Cork. “Early gut bacteria regulate happiness.” ScienceDaily. ScienceDaily, 12 June 2012. www.sciencedaily.com/releases/2012/06/120612115812.htm[↩]
  11. The Mount Sinai Hospital / Mount Sinai School of Medicine. “Transfer of gut bacteria affects brain function, nerve fiber insulation.” ScienceDaily. ScienceDaily, 20 April 2016. www.sciencedaily.com/releases/2016/04/160420104209.htm[↩]
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  14. Guo H, et al. Akkermansia muciniphila Improves Depressive-Like Symptoms by Modulating the Level of 5-HT Neurotransmitters in the Gut and Brain of Mice. Mol Neurobiol. 2024 Feb;61(2):821-834.[↩]
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