Review of studies suggests a potentially useful link between gut bacteria and mental disorders. People who experience anxiety symptoms might be helped by taking steps to regulate the microorganisms in their gut using probiotic and non-probiotic food and supplements, suggests a review of studies published today in the journal General Psychiatry. Anxiety symptoms are common in people with mental diseases and a variety of physical disorders, especially in disorders that are related to stress. Previous studies have shown that as many as a third of people will be affected by anxiety symptoms during their lifetime. Recent research also suggests that mental disorders could be treated by regulating the intestinal microbiota, but there is no specific evidence to support this. Probiotics are living organisms found naturally in some foods that are also known as “good” or “friendly” bacteria because they fight against harmful bacteria and prevent them from settling in the gut. Overall, 11 of the 21 studies showed a positive effect on anxiety symptoms by regulating intestinal microbiota, meaning that more than half (52 percent) of the studies showed this approach to be effective, although some studies that had used this approach did not find it worked.