Probiotics reduce negative mood over time: the value of daily self-reports in detecting effects

Johnson KVA, Steenbergen L. Npj Ment Health Res. 2025 Apr 9;4(1):10.

A randomised, double-blind, placebo-controlled study in 88 healthy volunteers examined the effects of a multispecies probiotic on emotional regulation and mood. A combination of methods (questionnaires, emotional processing tests and daily reports) were used to capture how probiotics influence emotion and to provide insight into the psychological effects of taking probiotics in a young and healthy adult population (mean age 22.3 years).

A multispecies probiotic was administered for 28 days. Participants were instructed to take one sachet daily. Each sachet contained 2 g (2.5x10⁹ colony forming units [CFU] per gram) of freeze-dried powder of the probiotic mixture Ecologic® BARRIER (Winclove Probiotics B.V.). Ecologic® BARRIER contains nine bacterial strains: Bifidobacterium bifidum W23, B. lactis W51 and W52, Lactobacillus acidophilus W37, Levilactobacillus brevis W63 (formerly classified as Lactobacillus brevis W63), Lacticaseibacillus casei W56 (formerly classified as Lactobacillus casei W56), Ligilactobacillus salivarius W24 (formerly classified as Lactobacillus salivarius W24), and Lactococcus lactis W19 and W58.

Results

Daily reports

• The change in daily mood over time, as measured by visual analogue scale (VAS), revealed a reduction in negative mood in the probiotic group, particularly after the two-week mark. Interaction between group x time significantly predicted negative mood, according to regression models (p=0.009).

* Graph depicts the mean and standard error for negative mood, with the probiotic group shown in blue and the placebo group in red.

Questionnaires

• There was little evidence of differences between the probiotic and placebo groups in terms of the change in questionnaire scores following the intervention.
• Participants in the probiotic group scored lower on the not-distracting subscale of the multidimensional assessment of interoceptive awareness (MAIA) post-intervention whereas there was little change in the placebo group. This is indicative of the probiotic group showing a greater tendency to ignore or distract themselves away from sensations of pain or discomfort after the intervention compared to the placebo group (p=0.017).

Emotional processing

• There was a marginally significant (p<0.05) interaction between group and session, wherein the probiotic group showed improved accuracy in recognising facial expressions post-intervention. The authors suggest that this, when combined with the MAIA results, could indicate that probiotics may influence our ability to recognise emotions, both in oneself and others.

Predicting probiotic responders

• Six pre-intervention questionnaire scores showed some correlation (p≤0.08) with the change in daily negative feelings in the probiotic group. A linear model to predict the change in negative mood found that the main predictor of the change in negative mood was the Leiden index of depression sensitivity - revised (LEIDS-R) risk aversion subscale (p=0.013). LEIDS-R is considered a valid measure of cognitive vulnerability to depression.

Key Finding: This specific multispecies probiotic can benefit mental health in the general population by lessening negative mood, particularly after two-weeks of use. While changes in mood can be difficult to detect using standard pre-post questionnaires in a healthy population compared to those already suffering from psychological symptoms, daily mood (subjective) self-monitoring may serve as a more sensitive method to assessment. Early intervention with probiotics may provide a means to reduce the chances of developing clinical depression in certain at-risk individuals, such as those suffering from low mood who are also more averse to risk. Further research is required to understand such nuances as related to predicted treatment responders.