How Does Your Gut Microbiome Affect Your Brain?

Small but mighty, the microorganisms in your gut have a big influence on your mind

Christine Richmond

Updated March 06, 2025

An illustration of a silhouette of a human with a brain and intestines surrounded by gut bacterium

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Your remarkable, complex brain: It’s what makes you uniquely you. Your brain is shaped by your experiences and your genes. Along with, perhaps surprisingly, the microbes living in your colon.

It's astonishing but true. The community of bacteria, viruses and other microorganisms in your GI tract — your gut microbiome — exerts a lot of influence over your mind. In early childhood, your microbiome supports brain development. In adulthood, it affects how well you age and your risk of developing dementia. And every day, your microbiome communicates with your brain as part of a complex relationship known as the brain-gut connection.

The past two decades have seen an explosion of research on the subject. Scientists have made some fascinating, early discoveries, such as a 2018 study in which researchers transplanted gut microbes from severely depressed humans into healthy mice and saw that the mice, too, became anxious and depressed.

There's plenty more to learn, but the evidence thus far shows that a healthy gut microbiome could help protect the brain, while an unhealthy one (defined in part as lacking bacterial diversity, having more potentially “bad” microbes than “good” ones — or both of these things) might make a person more susceptible to inflammation and dementia. Here's a closer look at how your microbiome can influence five key aspects of your brain health.

Brain development

During your first few years of life, both your brain and your gut microbiome develop rapidly. In the brain, billions of neurons and trillions of the connections between them are developing. Scientists theorize that the developing brain may be especially sensitive to the neurotransmitters and other chemicals being made by the microbiome. The makeup of infants’ and toddlers’ microbiomes may be linked to the growth and function of brain areas associated with regulating emotions, language and motor skills, suggests a review of 20 human studies published in Developmental Review in 2022, but larger studies are needed to determine how this may affect brain health, both early and later in life.

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Behavior and personality

Your gut microbes may influence whether you’re a social butterfly or a wallflower. Personality traits like being extroverted, open to experiences and having an agreeable attitude were related to variations in gut microbiome composition in a study of 313 older adults in the Wisconsin Longitudinal Study published in 2020 in Brain, Behavior, & Immunity - Health. And sociability was associated with greater microbiome diversity in a study of 655 adults with a mean age of 42 living in 20 different countries published in 2020 in Human Microbiome Journal.

Mental well-being

Comparing the gut microbes of 48 people ages 55 to 85 — 32 with depression and 16 healthy controls — researchers found those with depression had an abundance of certain bacteria, reporting in the Journal of Psychiatry & Neuroscience in 2024. Similar findings have been shown in other studies; the gut microbiomes of people with depression were found to be significantly different than those of healthy controls in a systematic review of 43 studies involving 3,936 adults published in The International Journal of Molecular Sciences in 2022.

Emotional resilience

Healthy adults who are able to cope with and quickly recover from personal difficulties had microbiome characteristics linked to lower inflammation in a study of 116 adults ages 18 to 60 published in Nature Mental Health in 2024. The results suggest that “the microbiome is critical in shaping resilience,” the study authors note. Having a less diverse microbiome was associated with higher levels of stress in the Human Microbiome Journal study mentioned above.

Memory

Researchers were able to induce Alzheimer’s symptoms in healthy adult rats in a buzzworthy study published in 2023 in Brain that was similar to the depression research mentioned above. Rats that received gut microbes from people with Alzheimer’s disease performed significantly worse on memory tasks and produced fewer new nerve cells in the hippocampus, a part of the brain important to memory, compared with rats that received microbes from healthy humans.

As Alzheimer’s disease progresses, the gut microbiome changes, according to research from the Alzheimer Gut Microbiome Project (AGMP). Rob Knight, a co-principal investigator at AGMP, says that part of his work involves “looking at how particular microbes play a role in the development of plaques and tangles.” (Amyloid plaques and tau tangles are the hallmarks of the disease.) In other research, people with cognitive impairment had lower amounts of certain gut bacteria with anti-inflammatory properties, including Odoribacter, Butyricimonas and Bacteroides. Published in Translational Neurodegeneration in 2022, the study analyzed data from more than 1,430 adults age 45 to 72 as well as a separate cohort of 1,300 people ages 55 and up.