Probiotics improve mood in healthy adults

In a recent study published in the journal Mental Health Research, researchers found that probiotics can reduce daily bad mood in healthy people over time, although this effect has not been documented using standard psychological questionnaires.

Finding ways to promote mental health and prevent the onset of psychological symptoms has become increasingly challenging. Despite advances in neuroscience, psychology, and psychiatry, there is an urgent need for new effective interventions, including behavioral therapy, neurostimulation, nutritional supplements, and pharmacotherapy. Research has shown that gut microbial diversity can influence brain development, behavior, and neurochemistry.

In studies, it has been demonstrated that rodents that received gut microbiota from depressed individuals exhibited changes resembling depression at behavioral and physiological levels. Various human studies have reported that probiotics can alleviate symptoms of anxiety, stress and depression.

In this study, researchers evaluated the effects of probiotics on emotion regulation. People with a body mass index (BMI) of 18-30 kg/m², who had not taken probiotics or antibiotics in the past three months, and who were not taking any medications other than hormonal contraceptives for women were eligible to participate in the study; subjects who used drugs more than once a month or consumed more than 20 units of alcohol per week were excluded.

In addition, subjects with gastrointestinal, liver or kidney disease, central nervous system (CNS) disorders or trauma, psychiatric or psychological disorders, allergies or hypersensitivities to nutrients (e.g., soy, gluten), or who had participated in dietary programs within the past three months were excluded. Participants were randomized to receive probiotics or placebo for four weeks.

Probiotics came in the form of freeze-dried powder containing nine strains of bacteria. The placebo consisted of freeze-dried powder of maltodextrins and corn starch. In addition, participants completed several general emotion regulation questionnaires before and after the intervention.

A facial expression recognition task (FERT) analyzed the accuracy of emotion identification, and a dot probe task analyzed selective attention to emotional facial expressions. Participants also reported daily characteristics of their chair and mood. Experimental analyses determined whether pre-intervention questionnaire results could predict which individuals respond best to probiotics.

Overall, there was no evidence that probiotics had a positive effect on questionnaire measures of emotion; however, their administration was associated with a reduction in negative mood over time when assessing daily mood tracking. Despite the use of multiple questionnaires, the only post-intervention differences were the probiotic group’s lower scores on one subscale of the MAIA and the placebo group on the PSWQ.

The study authors emphasize that pre- and post-intervention questionnaires may not be sensitive enough to detect subtle emotional changes in healthy individuals, whereas daily mood tracking provides a more nuanced and time-intensive assessment. Notably, negative mood improved faster in more risk-prone individuals when taking probiotics.

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Published: 15.04.2025

Updated: 14.04.2025

Medical author, Medical editor:

Stepan Yuk

Medical expert:

PhD. Olexandr Voznyak