The Gut-Brain Connection to Anxiety

by Jerry Kennard, Ph.D. Medical Reviewer

Over the past few years there has been mounting evidence that bacteria in the gut can play a huge role in our overall mental health. Harmful bacteria is known to ramp up anxiety and several studies have shown that probiotics can have the opposite effect. It's a two-way street, says Dr. Siri Carpenter, writing for the American Psychological Association, just as bacteria in the gut seem able to influence the brain, so the brain can exert influence on the gut. Stress, for example, manages to suppress beneficial bacteria and opens the way for harmful bacteria to flourish causing inflammation and increased risk of infection. Some experts are now suggesting that people suffering from anxiety may benefit from eating more healthy bacteria in order to correct the imbalance that has accumulated in the gut.

The average adult carries around five pounds of bacteria in the gut and the effects of correcting bacterial imbalance can be dramatic according to a study published in Nutritional Neuroscience. In an interview with ABC news, Dr. James Greenblatt, a Boston-area psychiatrist, described how a simple urine test revealed elevated levels of HPHPA (a chemical byproduct of clostridia bacteria) in a teenager with obsessive-compulsive disorder and attention deficit hyperactivity disorder. He put the patient on an intensive dose of probiotics and after six months the symptoms began to disappear. Greenblatt says he now checks everyone in the same way and while "eight out of ten are fine, in the two patients where it's elevated, it can have profound effects on the nervous system."

Such findings appear to offer a tantalizing treatment but research into the gut-brain connection is still in its infancy. Certainly for a subset of people with anxiety or possibly even depression there may be relatively quick and useful outcomes by changing diet, but it's by no means a magic bullet. Everyone has their own unique system determined in part by genetics and in part by the bacteria that live in on and around us. Gut bacteria actually produce hundreds of neurochemicals that the brain then uses to regulate psychological processes like learning, memory and mood. Did you know, for example, that gut bacteria manufacture about 95 percent of the body's supply of serotonin?

Much of the research to date has been with animal studies and it looks like we're many years away from a time when doctors may routinely check our gut bacteria when we report symptoms of anxiety or depression. Even so there are increasing indications that healthy bacteria can reduce stress-induced hormones while increasing the expression of receptors for the neurotransmitter GABA, which helps to calm us.


Bravo, J.A. et al (2011) Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences.

Carpenter, S (2012) That Gut Feeling. APA, vol 43, No 8, page 50.

Jerry Kennard, Ph.D.
Meet Our Writer
Jerry Kennard, Ph.D.

Jerry Kennard, Ph.D., is a Chartered Psychologist and Associate Fellow of the British Psychological Society. Jerry’s work background is in mental health and, most recently, higher education. He is the author of various self-help books and is co-founder of