A new study published in npj Mental Health Research has found that probiotics may help reduce negative mood in healthy adults—though not in ways that traditional psychological assessments could detect.
Despite growing efforts to promote mental well-being and prevent the onset of psychological symptoms, scientists continue to seek new, effective interventions. This study highlights probiotics—a nutritional supplement known for its impact on gut health—as a potential tool to support emotional regulation through daily mood improvements.
Gut Health and Emotional Well-Being
Researchers have increasingly linked the gut microbiome to brain function, behavior, and emotional health. Past studies in animals have shown that gut bacteria transferred from depressed humans can induce depressive-like behaviors in rodents. Similarly, various human studies have reported improvements in anxiety, stress, and depression symptoms following probiotic use, although findings in non-clinical populations have been inconsistent.
Study Design and Methods
The recent double-blind, randomized, placebo-controlled trial sought to explore the effects of probiotics on emotion regulation in healthy adults. Participants, aged around 22 and with an average body mass index (BMI) of 23 kg/m², were screened for several exclusion factors, including recent use of antibiotics or probiotics, psychiatric disorders, or major health conditions.
A total of 88 individuals were randomly assigned to receive either a daily probiotic supplement or a placebo over four weeks. The probiotic supplement contained a blend of nine bacterial strains, including various types of Lactobacillus and Bifidobacterium, delivered in a freeze-dried powder form. The placebo consisted of a similar-looking powder made from maltodextrins and maize starch.
Before and after the intervention, participants completed several validated psychological assessments, such as the Center for Epidemiological Studies Depression Scale (CES-D), the Positive and Negative Affect Schedule (PANAS), and the Perceived Stress Scale (PSS), among others. In addition, participants took part in two cognitive tasks—the facial expression recognition task (FERT) and the dot-probe task—and provided daily reports on mood and bowel health.
Limited Changes on Standard Measures
Overall, the questionnaire results revealed little evidence of change in emotion regulation due to the probiotic intervention. The only statistically significant post-intervention difference observed was a reduction in worry (as measured by the Penn State Worry Questionnaire), which occurred only in the placebo group.
On the Multidimensional Assessment of Interoceptive Awareness (MAIA), the probiotic group scored lower on the “not-distracting” subscale, indicating a greater tendency to be distracted by discomfort or pain. However, this effect was modest, and no significant differences were observed in bowel health or cognitive task performance.
Notable Effects on Daily Mood
The most striking finding emerged from participants’ daily self-reports. While traditional questionnaires failed to detect meaningful emotional improvements, individuals taking probiotics reported a noticeable reduction in negative mood, especially after the first two weeks of supplementation.
This improvement, though modest, was consistent and measurable only through real-time, daily mood tracking—suggesting that standard psychological tools may overlook subtle emotional shifts in healthy populations.
An exploratory analysis further indicated that baseline emotional traits, particularly higher risk aversion as measured by the Leiden Index of Depression Sensitivity (LEIDS-R), were associated with a more pronounced benefit from probiotic supplementation.
Implications and Future Directions
The study authors conclude that while probiotics did not produce measurable changes on conventional psychological scales, they did have a tangible effect on participants’ daily mood. This underscores the potential of probiotics as a supportive tool for emotional wellness, even in those without clinical mental health conditions.
Importantly, the research highlights the value of daily self-monitoring tools in capturing nuanced emotional changes that broader assessments may miss. The findings also suggest that individuals with certain psychological traits—such as heightened risk aversion—could benefit more significantly from probiotic use.
As the gut-brain connection continues to draw scientific interest, the study adds to a growing body of evidence supporting the emotional benefits of probiotics and encourages more nuanced methods of tracking psychological well-being.
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