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- A study showed that taking a probiotic every day for two weeks helped reduce negative feelings in people.
- Tracking mood daily found small changes in how people felt that regular mental health surveys missed.
- Probiotics helped ease bad moods, but they didn’t make people feel more positive or change how their brains handled emotions.
- People who avoid risks got the most benefit. This suggests that future probiotic treatments for mental health might be made just for certain people.
- Eating foods good for the gut, like those with probiotics and prebiotics, might naturally help people feel more balanced emotionally.
Scientists are very interested in the connection between the tiny living things in your gut and your brain. They want to know what this connection might mean for mental health. New research has found a possible link between taking probiotics and actually feeling fewer negative emotions. This was seen especially when people used more sensitive ways to check their moods, like tracking them every day. This article talks about how the gut and brain work together, what a new study says about probiotics and how people feel, and if adding probiotics to your routine could lead to better emotional balance.
The Gut–Brain Axis: A Quick Look
The gut and brain are connected more closely than we used to think. The gut–brain axis is a complicated, two-way system that links your digestive system and your central nervous system. This system uses nerve, hormone, and immune paths. It also includes the nervous system in your gut, which is sometimes called the “second brain.”
Ways the gut and brain talk to each other include
- Vagus Nerve: This is the longest nerve in the head. It works like a major road sending signals from the gut to the brain and back again.
- Immune System: Gut bacteria affect swelling and how your body fights sickness. Both of these things are linked to how you feel mentally.
- Microbial Metabolites: Gut bacteria make things like short-chain fatty acids and brain chemicals such as GABA, dopamine, and serotonin. All of these play a part in how you feel.
It’s interesting that about 90% of the body’s serotonin—a brain chemical connected to feeling good and happy—is made in the gut, not the brain. This supports the idea that how you feel emotionally isn’t just about what’s going on in your mind. It is also tied to the conditions inside your body, including the mix of tiny living things in your digestive system.
Why Mental Health Experts Care About Probiotics
Many people around the world have mood problems like anxiety and depression. This shows how important it is to find safe, easy-to-get, and helpful ways to improve mental health. Regular treatments like SSRIs and talking therapy don’t work completely for everyone. So, researchers are looking at the gut for answers.
Probiotics are live tiny living things that are good for health when you eat enough of them. They seem like a good possibility. Taking these supplements can change the types of microbes in your gut. This, in turn, might affect how you manage your feelings. Probiotics are found in foods like yogurt and kefir and also in pills. People are starting to see them not just as something to help with digestion, but as something that might help change your mood.
Many science studies, including controlled trials where people are randomly put into groups, have tried to see if probiotics help reduce negative emotions, make people feel better, and ease signs of depression and anxiety. But the results have not always been the same. Some studies report they help a lot. Others find they don’t do much.
This difference in results led researchers like Dr. Katerina Johnson to find better ways to check how people’s feelings change over time, in their normal lives.
New Study Shows Why Tracking Daily is Better Than Standard Questionnaires
The recent study from npj Mental Health Research is different because it looked at both whether probiotics affect mood and how we measure that effect.
The study was done in a way where neither the people in the study nor the researchers knew who was getting the real probiotic. People were put into groups by chance. 88 healthy young adults took part. For four weeks, participants took either a probiotic supplement—a mix of nine types of bacteria often found in the human gut—or a fake pill.
What made this study different was not just giving the supplement, but the way mood was checked
- People reported how they felt every day using a phone app.
- Each day, they rated how strong their negative and positive feelings were at that moment.
This detailed information gave a more immediate and real picture of what people felt in their daily lives. This is very different from standard psychology tests, which ask people to think back over longer times. Thinking back like that usually means people don’t report their feelings as accurately.
Main Findings: Small but Important Emotional Changes
After taking the probiotic every day for two weeks, a clear pattern was seen: People taking the probiotics started to report fewer negative emotions.
Specific negative feelings that got better included less
- Sadness
- Irritability
- Anxiety
- Emotional tiredness
Interestingly, positive feelings like feeling excited, joyful, or happy didn’t go up much. This is an important point. The supplements didn’t make people feel overly happy or manic. Instead, they seem to work like a buffer, making negative feelings happen less often and be less strong.
“Probiotics may have promise in preventing low mood progressing to mental health conditions like depression.” – Katerina Johnson
These early signs could mean that in the future, probiotic supplements might be used as part of overall care to help prevent mental health issues, especially for people who don’t have a clear diagnosis but often feel down.
Standard Mood Tests Might Not Catch the Small Changes
Besides the daily phone mood check, participants also filled out regular psychology tests at the start and end of the study. These tests looked at bigger issues like depression, general stress, and anxiety.
It was surprising that these tests did not show big differences between the group that got the fake pill and the group that got the probiotic. In some areas, the fake pill group even seemed a little better.
So, why is this? There are a few good reasons
- Putting Everything Together: The tests combined weeks of feelings into one score, hiding changes that happened slowly.
- Remembering Things Wrong: People remember how they felt with a bias. Their current mood often changes how they remember the past, not how they actually felt over many days.
- Tests Look for Different Things: Standard tests are meant to find specific mental health problems. They don’t capture the small changes in how people feel day-to-day.
But, the daily tracking method did pick up on these smaller feeling changes. This might be why previous studies might have “missed” the effects of probiotics: they used rough, one-time tests instead of checking feelings as they happened over time.
Who Gets the Most Help? How Personality Traits Matter
One important part of the study was that the effects were different for people with certain personality traits. People who were more risk-averse—a trait linked to feeling emotions more easily—seemed to get the most help from taking probiotics.
This means a lot
- It suggests that how well probiotics work on mood depends on a mix of body factors and personality traits.
- Risk-averse people might have stronger stress responses or parts of their brain (like the amygdala) that react more. Probiotics could help protect against this by making the gut-brain signals more steady.
- This opens the door for mental health plans made just for you. Probiotic use could be based on your personality.
Knowing this might one day help doctors suggest certain types of probiotics to people based on their specific emotional needs.
Gut Feeling Versus Brain Work: No Change in Thinking Tasks
Even though people felt better emotionally, they didn’t do better on thinking tasks related to emotions. When tested on things like recognizing faces or reacting to emotional pictures, both the fake pill group and the probiotic group did about the same.
This suggests that while people felt better subjectively, they didn’t get better at consciously understanding emotions.
What this might mean
- Emotional changes happened mostly on a feeling level, not a thinking one.
- These effects might come from changing mood without thinking about it, through gut microbe pathways, instead of thinking about feelings in a planned way.
This split further supports the idea that probiotics work on brain chemical paths that don’t involve conscious thinking. They affect parts of the nervous system that change how we “feel” rather than how we “think about” feelings.
Timeframe Matters: Like Antidepressants
Another interesting point about the study was when people started to feel better. The good effects of taking probiotics started to show up around day 14. This is about the same time that certain antidepressants, like SSRIs (which are often prescribed), usually start to work.
This timing overlap might give us hints about paths in the body that are the same
- Reducing Swelling: Both antidepressants and probiotics seem to reduce swelling in the body. They lower markers like IL-6 and TNF-alpha.
- Making Brain Chemicals: Some gut bacteria directly make or help make serotonin.
- Activating Vagus Nerve: Studies show both medicines and microbes can affect the vagus nerve’s activity. A strong vagus nerve activity is linked to being able to handle stress better.
Even though both treatments work in different ways, their timing is similar. This suggests they could work together to help keep mood steady.
Why Past Studies Had Different Results
It has been tricky in the field of probiotics for mental health because study findings have been so different. What we now know is that how a study is done matters. Just looking at the start and end of a treatment can hide real changes in how people feel over time.
Other reasons for results not matching include
- Differences in the types of probiotics used (not all types affect the brain in the same way).
- Different amounts or lengths of time the probiotics were used.
- Using too simple ways to measure results that don’t catch changes in feelings that happen slowly.
This newest study shows the way for more detailed methods that check things in the moment for future studies. Understanding mood isn’t just about two opposite states. Looking at it like that doesn’t do justice to how complex the human mind is.
Probiotics from Food Versus Supplements
Probiotic supplements are easy to get and more science is showing they help. But they are not the only way to get probiotics.
Natural sources of probiotics include
- Yogurt (that has live cultures)
- Kimchi and sauerkraut (foods made by natural process)
- Aged cheeses
- Kefir, a milk drink made by process with many different types of microbes
For benefits that last, it’s best to have probiotics with prebiotics. These are plant fibers that feed your good gut bacteria.
Top prebiotic foods include
- Bananas
- Onions, garlic, and leeks
- Whole grains like oats and barley
- Legumes and lentils
Together, probiotic + prebiotic = synbiotic. This is a strong mix that helps both gut health and possibly keeps mood balanced [(Sonnenburg & Sonnenburg, 2019)].
What This Means in Real Life: Should You Take Probiotics for Mood?
What’s the conclusion? If you are generally healthy but sometimes feel moderately down, adding probiotic supplements might offer a gentle way to help your mental state over time.
Things to think about
- Check how you feel emotionally every day—this helps you notice things and see patterns as they start.
- Pick a good quality probiotic with several types of microbes that science studies have shown work.
- Have supplements along with a diet high in fiber and different kinds of foods to feed your gut microbes.
- Always talk to a doctor or other healthcare provider if you have current mental health conditions.
Keep in mind: Probiotics won’t cure things. But they could be a safe way to help reduce negative emotions. This is especially true if they are used in a way that fits your personal traits or lifestyle.
Study Limits and What Future Research Should Do
While the findings look good, they need to be understood based on the study’s limits. Main limits include
- Small number of people in the study (88)
- Not many different kinds of people (mostly young, healthy adults)
- Using ways for people to report things themselves. Even though these reports were detailed, they aren’t standard ways to diagnose problems.
Future research should look at
- Different groups of people, including older adults and people with mood problems that have been diagnosed.
- Studies that last longer, over many months or even years.
- Body markers like cortisol (a stress hormone), markers for swelling in the blood, and checking the types of gut bacteria to see which specific types work best.
If this works, it could lead to a time of targeted therapy using microbes. Supplements would be matched to each person’s body and mind. This could really change how we deal with everyday mental well-being.
Could Probiotics Play a Part in Mental Health?
Yes, definitely—but not on their own. More and more evidence supports including the gut–brain axis when talking about how people feel emotionally. While more solid studies are needed, using probiotic supplements might be a low-risk way to help for people who want to feel fewer negative emotions and be more able to handle stress.
Equally important: learn about your feelings. By tracking mood daily, being more aware of yourself, and taking care of your gut with food and, if right for you, supplements, you build a stronger base for long-term mental health.
Citations
- Johnson, K. V.-A., & Steenbergen, L. (2024). Probiotics reduce negative mood over time: the value of daily self-reports in detecting effects. npj Mental Health Research. https://doi.org/10.1038/s44184-025-00123-z
- Johnson, K. V.-A. (n.d.). [Personal commentary via interview].
- Sonnenburg, E. D., & Sonnenburg, J. L. (2019). The ancestral diet meets. Cell Host & Microbe, 25(4), 553–564.
- Mayer, E. A., Tillisch, K., & Gupta, A. (2015). Gut/brain axis and the microbiota. The Journal of Clinical Investigation, 125(3), 926–938. https://doi.org/10.1172/JCI76304
