People focus less on bad feelings and experiences from the past, which psychologists refer to as rumination, following four weeks of probiotics administration, according to psychologists Laura Steenbergen and Lorenza Colzato from the Leiden Institute for Brain and Cognition.

Probiotics are live microorganisms which, when administered in adequate amounts, are fundamental in improving digestion and immune function as part of the human microbiome.

Steenbergen and her team were the first to investigate whether the administration of probiotics containing different strains for at least 4 weeks has a beneficial effect on rumination.

Predictive Depression Marker

Rumination, recurrent thoughts about possible causes and consequences of one’s problems, according to Steenbergen is:

“one of the most predictive vulnerability markers of depression. Persistent ruminative thoughts often precede and predict episodes of depression."

Steenbergen directed the forty healthy subjects participating in the research to take a sachet containing powder which was mixed with lukewarm water or milk each day of the intervention.

Half of the people received a placebo powder, while the other half received the probiotics mixture. People were invited to the lab twice; one time at the begin of the intervention and the second time after 4 weeks when the intervention was completed.

On both occasions they were required to fill in a questionnaire measuring cognitive reactivity- sensitivity - to depression.

Compared to subjects who received the placebo intervention, participants who received the multispecies probiotics intervention showed significantly reduced ruminative thoughts. Colzato:

“Even if preliminary, these results provide the first evidence that the intake of probiotics may help reduce negative thoughts associated with sad mood. As such, our findings shed an interesting new light on the potential of probiotics to serve as adjuvant or preventive therapy for depression."


Laura Steenbergen, Roberta Sellaro, Saskia van Hemert, Jos A. Boschd, Lorenza S. Colzato “A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood.” Brain, Behavior, and Immunity, April 2015, doi:10.1016/j.bbi.2015.04.003

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