Probiotics and Well-Being: Relief From Stress and Anxiety in Just Two Weeks

Daily use of probiotics for four weeks helped reduce negative mood in healthy young adults. The effects began to appear after two weeks, especially when assessed with daily monitoring. The study suggests that probiotics may play an important role in emotional health, even in people without mental disorders.

In recent years, many people have been looking for ways to better take care of their mental health and prevent the onset of symptoms such as anxiety, stress and depression. Despite advances in areas such as psychology, psychiatry and neuroscience, it is still important to find new forms of treatment, from medications and therapies to changes in diet.

A topic that has aroused a lot of interest is the intestinal microbiome, the set of billions of microorganisms that live in our intestines. Research has shown that these microorganisms can affect brain function, behavior and even emotions.

In studies with animals, for example, it has been possible to observe that when transferring the intestinal bacteria of a depressed person to a rat, the animal also begins to exhibit behaviors similar to depression.

These effects occur because the intestine communicates with the brain through nerve pathways, the immune system and hormones. It has been proven, for example, that certain probiotics (the “good” bacteria found in supplements or fermented foods) can reduce symptoms of anxiety and depression in animals, but only when the nerves that connect the intestine to the brain are working.

These probiotics also appear to reduce inflammatory substances and stress hormones, both in animals and in humans. In view of this, researchers at Leiden University in the Netherlands decided to investigate whether the use of probiotics could also bring emotional benefits to healthy people, especially with regard to emotional regulation, the ability to deal with intense emotions, such as sadness or anger.

This is important because difficulties in regulating emotions are present in several mental disorders. To do this, a study was conducted with healthy young adults. The participants could not have recently taken antibiotics or probiotics, nor have chronic diseases, psychological problems, frequent use of alcohol or drugs, or severe dietary restrictions. In total, around 90 volunteers were selected.

The study was conducted very rigorously: participants were randomly divided into two groups. One group took a powdered probiotic (containing 9 different types of bacteria) for 28 days, and the other group took a placebo (a powder with no effect, but with an identical appearance and taste to the probiotic).

No one, neither the participants nor the researchers, knew who was taking what until the end of the experiment. This is called a “double-blind” study, and it serves to ensure that the results are not influenced by expectations. Before starting and after finishing the 28 days, everyone took the same emotional tests and answered questionnaires.

During the four weeks, they also filled out a simple diary every day, reporting how they were feeling. This helped the scientists to track changes in mood over time more accurately. The main result was that, even in people without psychological problems, probiotics helped to reduce negative moods from the second week of use.

However, when the researchers compared only the tests done before and after treatment (as most studies do), few changes appeared. This shows that daily monitoring was essential to see the real effects.

Change in daily mood scores during the 4-week intervention. The graphs show the mean and standard error for negative mood and positive mood, with the probiotic group shown in blue and the placebo group in red.

In summary, the study suggests that probiotics can improve emotional health even in healthy people, although the effect is more subtle and better seen with more frequent assessment tools.

The researchers believe that in the future it will be possible to better identify who benefits most from probiotics, and perhaps use them as part of prevention in people at higher risk of developing emotional problems.

READ MORE:

Probiotics reduce negative mood over time: the value of daily self-reports in detecting effects

Katerina V.A. Johnson, and Laura Steenbergen

npj Mental Health Res 4, 10 (2025)

https://doi.org/10.1038/s44184-025-00123-z

Abstract:

The burgeoning field of the microbiome–gut–brain axis has inspired research into how the gut microbiome can affect human emotion. Probiotics offer ways to investigate microbial-based interventions but results have been mixed, with more evidence of beneficial effects in clinically depressed patients. Using a randomised, double-blind, placebo-controlled design in 88 healthy volunteers, we conduct a comprehensive study into effects of a multispecies probiotic on emotion regulation and mood through questionnaires, emotional processing tests and daily reports. We find clear evidence that probiotics reduce negative mood, starting after two weeks, based on daily monitoring, but few other changes. Our findings reconcile inconsistencies of previous studies, revealing that commonly used pre- versus post-intervention assessments cannot reliably detect probiotic-induced changes in healthy subjects’ emotional state. We conclude that probiotics can benefit mental health in the general population and identify traits of individuals who derive greatest benefit, allowing future targeting of at-risk individuals.