Gut microbiome may have tie to mental health

Dear Doctor:

I've been on a few different medications for depression, but none of them did much of anything. A friend keeps going on about psychobiotics, which to me doesn't even sound like a real word. What is he talking about?

Dear Reader:

Unfortunately, it's true that antidepressants don't work for everyone. This makes treating the estimated 16 million Americans who experience at least one major depressive episode each year an ongoing challenge. A study funded by the National Institutes of Health found that only one-third of individuals diagnosed with depression found complete relief through the first course of medication that they were prescribed.

As has happened with you, people living with depression often try several different medications — or combinations of medications — in a trialand-error search for a treatment that works. Even when antidepressants are successful at relieving symptoms, they come with an array of potential side effects, both physical and emotional. And when an antidepressant does work, it's possible for the patient to build up a tolerance. As a result, the drug becomes less effective over time.

All of this has caused scientists to keep seeking effective treatments. An important area of research pertains to something called the "gut microbiome." As scientists learn more about the importance of the trillions of microorganisms living in our bodies, they have established a connection between our guts and our brains.

New research shows that the makeup of the gut microbiome plays a significant role not only in mental health, but in cognition as well. The channel of communication runs both ways — the gut influences the brain, and the brain influences the gut. One theory is that the vagus nerve, which runs from the brain to the gut, acts as an information highway, with messages traveling in both directions. Some scientists have referred to the gut as our "second brain."

Out of these findings has come the term "psychobiotics," the one your friend used. Specifically, it refers to the types of live bacteria, or probiotics, that impart positive mental health benefits. Research in mice has shown that infusions of beneficial bacteria to the gut resulted in markedly lower levels of inflammation in the brain. This, in turn, influenced behavior, including lower levels of anxiety and fear when the mice made their way through a stressful maze.

Scientists are still figuring out how these findings in animal studies translate to humans. Someday antidepressants may consist of doses of feel-good bacteria tailored to the needs of each person's particular gut microbiome. In the meantime, the goal is to develop and maintain a gut microbiome that's robust and diverse. This is achieved by eating a high-fiber, low-sugar diet that's filled with plant-based and fermented foods. Exercise has been shown to be helpful to the gut microbiome, too.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.