New research suggests that probiotics may help reduce daily negative emotions, even if traditional psychological assessments fail to capture the shift.
In a recent study published in npj Mental Health Research, scientists found that probiotics may subtly improve emotional well-being in healthy individuals over time. While standard psychological questionnaires showed little change, participants who took probiotics reported reduced negative mood in daily self-assessments.
The findings add to growing evidence that the gut-brain axis plays a critical role in mental health. Though mental health interventions have evolved to include a wide range of strategies—from behavioral therapy to pharmacological treatments—experts continue to search for novel, accessible methods to support psychological well-being. Increasingly, the gut microbiome has come under scientific scrutiny for its potential influence on behavior and brain function.
Previous research in rodents has shown that gut bacteria from humans with depression can induce depression-like behaviors in animals. Meanwhile, human trials exploring the effects of probiotics on mood disorders have yielded mixed results, particularly in individuals without clinical diagnoses.
Study Design
The recent trial aimed to evaluate whether probiotics could influence emotional regulation in non-clinical populations. Researchers enrolled participants aged 18 to 30 with a body mass index (BMI) between 18 and 30. Exclusion criteria included recent use of antibiotics or probiotics, chronic illnesses, psychiatric conditions, or use of medications (with the exception of hormonal contraceptives for women). Participants with high alcohol or recreational drug use were also excluded.
Eighty-eight healthy adults were randomly assigned to receive either a probiotic supplement or a placebo for four weeks. The probiotic formula included a blend of nine bacterial strains, such as Lactococcus lactis, Lacticaseibacillus casei, and Bifidobacterium bifidum. The placebo contained maltodextrins and maize starch.
Participants completed a battery of validated psychological assessments before and after the intervention. These included the Positive and Negative Affect Schedule (PANAS), the Center for Epidemiological Studies Depression Scale (CES-D), and the Penn State Worry Questionnaire (PSWQ), among others. In addition, subjects took part in computer-based tasks to evaluate emotional perception and attentional bias and recorded their mood and gastrointestinal health daily.
Key Findings
The study found that standard questionnaire responses changed little after the four-week intervention. Notably, both groups experienced a decrease in worry, but only the placebo group’s reduction reached statistical significance.
The probiotics group did show a lower score on the “not-distracting” subscale of the Multidimensional Assessment of Interoceptive Awareness (MAIA), suggesting a greater tendency to disengage from discomfort or physical sensations post-intervention.
There were no significant changes in bowel habits, stool consistency, or selective attention to emotional cues in the dot-probe task. However, during the facial emotion recognition task (FERT), participants demonstrated better accuracy in identifying emotional expressions after the intervention. This improvement was slightly more pronounced in the probiotics group.
Critically, while the formal assessments showed modest effects, daily mood tracking revealed a clearer trend: those in the probiotics group reported a gradual decrease in negative mood—particularly noticeable after two weeks of supplementation. These self-reported improvements were not reflected in standardized testing, highlighting a potential gap in current psychological evaluation methods.
Exploratory analyses also indicated that individuals’ baseline psychological profiles may predict how responsive they are to probiotic intervention.
Implications
The study suggests that while probiotics may not produce dramatic changes detectable by conventional psychological questionnaires, they could offer subtle benefits in emotional resilience for otherwise healthy individuals. The results reinforce the importance of incorporating real-time mood tracking into mental health research and open the door for more personalized probiotic therapies.
Researchers emphasize that these findings are preliminary and that further studies are needed to confirm the efficacy and mechanisms of probiotic interventions in mental health care.
