4 Charts | How the Microbiome Affects Emotions | Visualized Science

Reviewed by The Clinical Committee

June 19, 2019

  • Bacteria may play a role in how we develop emotionally.

  • The types of bacteria in a baby's belly correlate with temperament.

  • Certain bacteria have been linked to fearfulness and sadness.

Microbiome & Positivity

How the microbiome affects positivity

Figure 1: How the microbiome affects positivity. Bifidobacterium, a type of bacteria in the actinobacteria class, has been shown to correlate with positivity. Infants with an abundance of actinobacteria had more outgoing and spontaneous personalities. This result was highly significant with a 0.000034 false discovery rate.

Your gut bacteria are more important than you think.

A new study finds that the microbiome may influence how personality develops in infants.

Researchers collected bacteria in poop samples from 301 infants and sequenced the bacterial DNA. This allowed them to see which types of bacteria were in each infant.

Infant Microbiome

Infants receive their gut bacteria from their mother. They are born with a mostly sterile gut devoid of bacteria. As they pass through the birth canal and reach the outside world, they acquire bacteria which go into the intestines and grow. The infant’s gut bacteria is highly influenced by the bacteria living on the mother.

Gut Microbiome

The gut microbiome refers to all the bacteria in your small and large intestines. Healthy individuals have lots of bacteria living in the intestines. Most of the time, these bacteria are not harmful. In fact, they have been shown to be essential for many life functions. For example, they are believed to crowd out some harmful types of bacteria such as clostridium difficile.

One of the strongest associations found was between bifidobacterium and surgency, a key infant personality traits used by experts. Surgency is an infant temperament trait that refers to positivity, cheerfulness, spontaneity, and sociability.

Babies who were more positive and spontaneous had significantly more bifidobacterium in their gut. This type of bacteria harmlessly lives in our bellies. This association suggests that this bacteria may play a role in positive and outgoing personalities.

False Discovery Rate

False discovery rate refers to the chances that a certain finding is the result of random chance alone. This is similar to p-value in that it measures the odds of a certain finding being real. However, unlike p-value, false discovery rate accounts for multiple experiments and samplings.

Source: Gut microbiota composition is associated with temperament traits in infants

Emotional Regulation & The Microbiome

Emotional Regulation & The Microbiome

Figure 2: Emotional Regulation & The Microbiome. Erwinia bacteria were found to correlate highly with emotional regulation. Infants who had greater emotional regulation were more likely to have an abundance of erwinia. This finding was significant with a false discovery rate of 0.04.

A baby’s ability to regulate their emotions was found to correlate with the amount of erwinia in their gut. Babies with these bacteria were more likely to be mellow and soothable. If you’ve ever met a “chill” baby, they may have had more erwinia.

Source: Gut microbiota composition is associated with temperament traits in infants

Negative Emotions & The Microbiome

Negative Emotions & The Microbiome

Figure 3: Negative Emotions & The Microbiome. Babies with more sadness and frustration tended to have more Serratia in their microbiome. This was a highly significant association with a false discovery rate of 0.002.

Not all bacteria are as positive as bifidobacterium or erwinia. Babies with another form of bacteria called serratia were more likely to have negative emotionality. This refers to the tendency of a baby to have negative emotions such as sadness and frustration.

Fear & The Microbiome

Fear & The Microbiome

Figure 4: Fear & The Microbiome. Rothia type bacteria were associated with more fear reactivity in infants. This was a significant result with a false discovery rate of 0.021.

Fear had its own bacteria as well. Babies who are more fearful or had a stronger tendency to respond with fear tended to have a lot more rothia type bacteria in their gut.

Keys to Health

This study provides a fascinating look into the link between gut bacteria and personality.

What is unclear at this point is causality. Does the presence of certain bacteria cause changes in personality, or are babies with certain personalities more likely to have certain gut bacteria? We will need further research to answer this.

What we do know is that bacteria are much more important than we had thought. Somehow, these bacteria in your belly are linked to personality.

Evidence Score:


Strength of Findings - Researchers found very clear findings with strong statistical significance. These findings are relevant, though not immedietaly applicable at this point.


Sample Size - The study used a large enough sample size to find clear evidence on bacteria and temperament.


Study Method - Researchers measured temperament by surveying mothers. While this is the most feasible way to measure temperament, it introduces significant potential of bias. A mother's opinion of their child may be highly dependent on the mother herself as well as the child's personality.

Expert Opinions


The brain is the most complex object in the known universe so how could it be reacting to bacteria in the gut? One route is the vagus nerve, it's an information superhighway connecting the brain and the gut. Bacteria break down fibre in the diet into chemicals called short-chain fatty acids, which can have effects throughout the body. There is even emerging evidence that gut bugs could be using tiny strips of genetic code called microRNAs to alter how DNA works in nerve cells.

Harvard Health

When we consider the connection between the brain and the gut, it’s important to know that 90% of serotonin receptors are located in the gut. In the relatively new field of nutritional psychiatry we help patients understand how gut health and diet can positively or negatively affect their mood. When someone is prescribed an antidepressant such as a selective serotonin reuptake inhibitor (SSRI), the most common side effects are gut-related, and many people temporarily experience nausea, diarrhea, or gastrointestinal problems.

American Psychological Association

In just the last few years, evidence has mounted from studies in rodents that the gut microbiome can influence neural development, brain chemistry and a wide range of behavioral phenomena, including emotional behavior, pain perception and how the stress system responds.

Clearvue Health is not affiliated with above organizations. The information above is provided to highlight and link to useful further reading.

Microbiome & Autism

Did you know that the microbiome may play a role in autism? A recent study out of Harvard found that the microbiome has a strong effect on child development. The different types of bacteria a child has in their gut correlates with how they will develop physically and behaviorally. Kids with lots of clostridiales bacteria in their guts were shown to have approx. 1.96x the odds of delayed social skills (95%CI = 1.22-3.15).

Microbiome and social development in kids

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