This was an interesting read and another reason to take probiotics or eat yogurt. Turns out probiotics, the kind you find in yogurt have a profound effect on the brain and moods! Here is the article.
"When Mr. Bravo looked at the brains of the mice, he found that those fed probiotics had more GABA receptors in areas associated with memory and the regulation of emotions. (This change mimics the effects of popular antianxiety medications in humans.)"