A new study suggests that there may be an effective alternative to medication for the treatment of depression: probiotic bacteria found in yogurt.
Researchers found that Lactobacillus - "friendly" bacteria present in live-cultured yogurt - reversed depressive-like behavior in mice by altering their gut microbiome, the population of microorganisms that reside in the intestines.
The study authors - from the University of Virginia School of Medicine - believe it is possible that the probiotic could do the same for humans.
"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," says lead researcher Alban Gaultier, Ph.D., of the Center for Brain Immunology and Glia at Virginia.
"It would be magical just to change your diet, to change the bacteria you take, and fix your health - and your mood," he adds.
An increasing number of studies have indicated that the gut microbiome plays a significant role in mental health. Research published in 2014, for example, found that probiotics - which boost the abundance of friendly gut bacteria - reduced anxiety and stress in adults.
Low Lactobacillus levels led to depression-like symptoms in mice
For this latest study - published in the journal Scientific Reports - Gaultier and team sought to determine if and how the gut microbiome plays a role in depression.
First, the researchers analyzed the gut microbiome of mice before and after they were exposed to stress. "When you're stressed, you increase your chance of being depressed, and that's been known for a long, long time," notes Gaultier.
The team found that stress led to the loss of Lactobacillus in the rodents' guts, and this led to the onset of depression-like symptoms.
Further investigation revealed that levels of Lactobacillus in the gut influence levels of a blood metabolite called kynurenine, which previous studies have associated with the development of depression.
In this study, when Lactobacillus levels in the mice were decreased, levels of kynurenine increased, and this led to the development of depression-like symptoms.
"This is the most consistent change we've seen across different experiments and different settings we call microbiome profiles," says study co-author Ioana Marin, also of the Center for Brain Immunology and Glia. "This is a consistent change. We see Lactobacillus levels correlate directly with the behavior of these mice."
Lactobacillus supplementation reversed depression-like symptoms
Next, the researchers supplemented the diets of the stressed mice with a strain of Lactobacillus called Lactobacillus reuteri for 3 weeks.
Not only were the rodents' Lactobacillus levels replenished as a result, but their depression-like symptoms were also reversed.
These findings indicate that including Lactobacillus in the diet has the potential to treat depression by increasing kynurenine levels, though the researchers caution that much more research is needed to confirm this theory.
"There has been some work in humans and quite a bit in animal models talking about how this metabolite, kynurenine, can influence behavior," notes Marin. "It's something produced with inflammation that we know is connected with depression. But the question still remains: How? How does this molecule affect the brain? What are the processes? This is the road we want to take."
In the meantime, the researchers say that there is no harm in patients with depression including yogurt in their diet. However, they stress that these individuals should not discontinue any medications without talking to their doctors.