Probiotics have been rising stars in the world of health in the last five years or so. The “good” bacteria that live in our gastrointestinal system contribute not only to digestion; they also influence the disorders and diseases we may develop, from inflammatory bowel disease (IBD) to cancer.

The delicate balance of gut microbes can be disrupted by infections like stomach bugs and taking antibiotics, but there’s good evidence that probiotics can help reset the body's bacterial balance. That's why many people take them intentionally — eating yogurt, other cultured and fermented products, or supplements — to ensure optimal physical health.

The new study suggests that probiotics might be used to treat depression. This would mean that the bacteria are not only ‘probiotic,’ but might also be considered ‘psychobiotic.’

Now it appears our bodies' microbial menagerie may influence our mental health as well.

There’s been some evidence that good bacteria in yogurt can affect brain function in people, and the new study suggests that they might actually be used to treat depression someday. This would mean that the bacteria are not only “probiotic,” but might also be considered “psychobiotic.”

The researchers from Ireland noted one study in particular, which looked at rat pups which had been separated from their mothers – a stressful event – and exhibited signs of depression. The team gave some of the rat pups a probiotic (Bifidobacterium infantis) for an extended period of time and then looked at their behavior, their immune systems, and the levels of certain brain chemicals.

Not only did the rat pups treated with the probiotics seem less depressed afterwards, but their immune function also improved, as did the level of a brain chemical, norepinephrine, which is linked with well-being.

The authors aren’t sure how probiotics might exert their effects, but they say it might be through the reduction of inflammation, which has previously been linked with depression and a host of other disorders.

The team is cautious about celebrating the effects of probiotics on mental health too soon, especially since few strains have been shown to have an effect: “What is clear at this point is that, of the large number of putative probiotics, only a small percentage have an impact on behaviour and may qualify as psychobiotics,” said study author Timothy Dinan in a news release.

But they’re optimistic about the possibility in the future, since more studies are suggesting that there may be a very real link between probiotics, mood, and the brain.

Always talk with your doctor before beginning to take a supplement, probiotics included. But most health officials agree that low-fat dairy products can be part of a healthy diet. So if you’re interested in adding them to your routine, make sure your yogurt says that it contains “live and active” yogurt cultures, as most do. Over time, you may find that your gut and your brain feel a difference.

The study was carried out by a team at University College Cork in Ireland and published in the journal Biological Psychiatry.