According to new research, the answer to depression and anxiety might be hiding in our guts.

Probiotics are good for the gut, but new research suggests that Lactobacillus—a probiotic bacteria found in yogurt—may reverse depression symptoms and anxiety. Researchers at the University of Virginia found that lactobacillus fed to mice could alleviate their symptoms of depression that had been induced in the lab.

They were able to identify the biological process responsible for the effect on mood—a direct link between the health of the gut microbiome and mental health—and believe the findings should hold true in people. "The big hope for this kind of research is that we won't need to bother with complex drugs and side effects when we can just play with the microbiome," explained lead researcher Alban Gaultier. "It would be magical just to change your diet, to change the bacteria you take, and fix your health—and your mood."

Depression, says Dr. Gaultier, "is a huge problem and the treatments are not very good, because they come with huge side effects."

The role of the gut microbiome—the bacteria that lives inside us—has been of tremendous interest to researchers studying depression and other health conditions, both mental and physical.

"When you're stressed, you increase your chance of being depressed, and that's been known for a long, long time," notes Dr. Gaultier. "So the question that we wanted to ask is, does the microbiome participate in depression?"

The answer appears to be yes.

Looking at the composition of the gut microbiome before and after mice were subjected to stress, Gaultier's team found that the major change was the loss of Lactobacillus. With the loss of lactobacillus came the onset of depression symptoms. Feeding the mice lactobacillus with their food returned them to almost normal. "A single strain of Lactobacillus," Gaultier observed, "is able to influence mood."

He and his team then went on to determine the mechanism by which Lactobacillus influences depression. They found that the amount of Lactobacillus in the gut affects the level of a metabolite in the blood called kynurenine, which has been shown to drive depression. When Lactobacillus was diminished in the gut, the levels of kynurenine went up—and depression symptoms set in.

Dr. Gaultier was careful to call the symptoms seen in mice as "depressive-like behaviour" or "despair behaviour," as mice have no way to communicate that they are feeling depressed. But those symptoms are widely accepted as the best available model for looking at depression in creatures other than humans.

Based on the new findings, Gaultier plans to begin studying the effect in people as soon as possible.

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