Can probiotics help treat depression and anxiety?

There is a lot of interest right now in the human microbiome (the populations of bacteria that live in various parts of the body, including the intestine, skin, and lungs). We now know that there are approximately 10 times as many bacterial cells as human cells in the body. The vast majority of these bacterial cells are in the intestinal tract, and they serve many purposes, including digesting foods, manufacturing certain vitamins (for example, vitamin K), and regulating our immune system. Researchers are actively studying whether changes in intestinal bacteria can increase the risk of chronic illnesses, such as obesity or inflammatory bowel disease.