With the gut-brain axis increasingly under scrutiny, two studies provide new evidence of how the microbiome, or gut bacteria, affects mental health. In a review in BMJ Nutrition Prevention & Health of seven high-quality probiotic and prebiotic studies, researchers found that 11 out of 12 probiotics studied produced “measurable reductions in depression.” The major strains studied were Lactobacillus acidophilus, L. casei and Bifidobacterium bifidum. In a second study in the journal Nutrients, 20 male soccer players ages 18 to 21 received either a placebo or a probiotics drink with L. casei for two months. By week four, those drinking the probiotic drink had significantly more relaxed (theta) and attentive (delta) brain waves, suggesting lowered anxiety and enhanced training ability. The probiotics drink also improved cognitive reaction time in the subjects.