There is growing interest in the possibility that probiotics improve not only gut health but also mental health.
Probiotics are "good" bacteria in the form of drinks or tablets that you can buy in the supermarket and are also found in foods like yogurts, fermented cheese and sauerkraut. There is growing interest in the possibility that probiotics improve not only gut health but also mental health. "The gut–brain connection provides various routes through which bacteria in the gut can influence how we feel and behave, including via the vagus nerve, immune system and hormones", says Johnson.
Daily mood reports
While animal studies have previously found promising effects of probiotics on the brain and behaviour, human studies have yielded inconsistent results. Johnson and Steenbergen therefore used a combination of methods to capture how probiotics might influence the ability to regulate our emotions and affect our moods. These included psychological questionnaires, daily mood reports and computer tasks testing how people process emotions. The study was conducted in young, healthy adults who took a probiotic (containing bacteria such as Lactobacillus and Bifidobacterium) daily for a month.
This is the first study to use daily mood reports to assess the effects of probiotics. It clearly shows that probiotics can reduce negative feelings compared to a placebo. This could mean a reduction in feelings such as anxiety, stress, fatigue or depressive tendencies. ‘It is striking that by simply asking participants how they were feeling each day, we could detect the beneficial effects of probiotics on mood’, says Steenbergen. ‘In contrast, the standard psychological questionnaires that are common in this field were not sensitive enough to pick up these changes.’
No substitute for antidepressants
The researchers found that it took about two weeks for the probiotics to improve negative feelings. It takes about the same amount of time for antidepressants to work, but whereas antidepressants tend to reduce both negative and positive mood, the results showed that the probiotics only reduced negative mood. This could be a possible benefit, although the researchers stress that probiotics should not be considered a substitute for antidepressants.
Who would benefit most from probiotics?
When the researchers observed the decrease in negative feelings, they were keen to explore whether they could predict who would benefit most from probiotics. "We found that various traits, most notably a propensity for risk avoidance, were associated with a greater effect of probiotics on mood", says Johnson.
In addition, the researchers found evidence that probiotics may affect the way participants process emotional cues. The participants who received probiotics were slightly more accurate at recognising facial expressions.
Probiotics could be used in a targeted way in the future
Many questions remain unanswered about how exactly probiotics work and their long-term effects. ‘Perhaps in the future probiotics could be used in a targeted way as an early intervention to reduce the chances of negative feelings progressing to mental health conditions such as depression, though more research would be needed to confirm that’, says Steenbergen.
Johnson and Steenbergen hope their findings will also spur other mental health researchers to include simple daily measures of mood in their studies. As they conclude in their paper, "In an attempt to delineate the complexity of the human brain and emotion, we cannot lose sight of asking the obvious. Sometimes the most simple questions reveal the most meaningful answers."
Reference: Johnson KVA, Steenbergen L. Probiotics reduce negative mood over time: the value of daily self-reports in detecting effects. npj Mental Health Res. 2025;4(1):1-9. doi: 10.1038/s44184-025-00123-z
This article has been republished from the following materials. Note: material may have been edited for length and content. For further information, please contact the cited source. Our press release publishing policy can be accessed here. Probiotics May Improve Mood Via Gut–Brain Axis | Technology Networks
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