Is yogurt beneficial for mental health? A team of researchers has identified how bacteria in fermented foods such as yogurt can help manage stress and prevent depression and anxiety.

The research team from the University of Virginia School of Medicine explored the influence of beneficial gut bacteria, called probiotics, on human behavior and how a lack of them can worsen depression and anxiety. The findings could pave the way for new therapies to treat anxiety, depression and other mental health conditions.

The study was published in the journal Brain Behavior and Immunity.

Yogurt is formed by fermenting milk. It contains streptococcus and lactobacillus strains of bacteria that are beneficial for gut health.

Previous studies have shown that in patients with depression and anxiety, gut bacteria, particularly those belonging to the Lactobacillus family, are disrupted. The condition is commonly referred to as dysbiosis.

Some clinical trials and animal studies have also shown that Lactobacillus has psychobiotic benefits, including stress resistance and reduction of disordered behavior in mice. They are also associated with reduced signs of depression and anxiety in patients.

In the latest study, researchers separated a collection of bacteria, known as Altered Schaedler Flora, from the gut microbiota that contains millions of bacteria, fungi and viruses. Altered Schaedler Flora contains two strains of Lactobacillus and six other bacterial strains.

"With this rarely used bacterial community, the team was able to create mice both with and without Lactobacillus, circumventing the need for antibiotics. Sure enough, the Altered Schaedler Flora produced exciting results," the researchers wrote in a news release.

"We were aware from our prior research that Lactobacillus was beneficial in improving mood disorders and was lost following psychological stress, but the underlying reasons remained unclear, primarily due to the technical challenges associated with studying the microbiome," said Alban Gaultier, lead researcher from UVA's Department of Neuroscience.

Prior research by Gaultier's team showed that Lactobacilli bacteria could reverse depression in lab mice. In the latest study, the team aimed to understand the mechanism by which Lactobacilli influence behavior, and how a lack of the bacteria can worsen depression and anxiety.

"Lactobacilli in the family Lactobaccillacea, they found, maintain the levels of an immune mediator called interferon gamma that regulates the body's response to stress and helps stave off depression," researchers explained.

"Our discovery illuminates how gut-resident Lactobacillus influences mood disorders, by tuning the immune system. Our research could pave the way towards discovering much-needed therapeutics for anxiety and depression," Gaultier said.

Researchers hope the findings will help formulate probiotics with optimum levels of Lactobacillus that could assist people struggling with or at high risk of depression.

"With these results in hand, we have new tools to optimize the development of probiotics, which should speed up discoveries for novel therapies. Most importantly, we can now explore how maintaining a healthy level of Lactobacillus and/or interferon gamma could be investigated to prevent and treat anxiety and depression," researcher Andrea R. Merchak said.

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