Recent research from the Netherlands’ Leiden Institute for Brain and Cognition has discovered that negative and aggressive thinking can be changed by supplementing with probiotic bacteria. The triple-blind study followed and tested 40 healthy people over a period of four weeks that were split into two groups; one was given a daily probiotic supplement containing seven species of probiotics and the other, a placebo.

The subjects filled out a questionnaire that measured cognitive reactivity and depressed moods using the Leiden Index of Depression Sensitivity, which measures negative and depressed thinking. After four weeks, the probiotic group showed significantly lower scores in aggression, control issues, hopelessness, risk aversion and rumination, compared

“The study demonstrated for the first time that a four-week, multispecies, probiotic intervention has a positive effect on cognitive reactivity to naturally occurring changes in sad mood in healthy individuals not currently diagnosed with a depressive disorder,” the researchers concluded.