Yogurt and Your Brain: New Evidence Suggests a Link Between Probiotics and Mental Health

By Tiago Palmisano
Edited by Bryce Harlan

It’s well known in the medical community that gut-bacteria produce beneficial effects. Commercials about probiotics – bacteria and yeast that provide benefits for human health– have become as prolific as prescription drug advertisements, and yogurts laced with specific strains of bacteria are now a fitness craze. Though generally thought to improve intestinal health, new research has shown that probiotics may also treat mental health diseases such as depression and autism.

Our intestinal tract contains more bacteria than our bodies contain cells. This diverse pool of prokaryotes makes its way into the intestines as soon as we are born, when we are exposed to the numerous organisms of the external world. Our relationship with bacteria persists throughout life, constantly involved in a delicate balance of chemical exchange. However, due to the location of bacteria in the digestive tract, the prescription of probiotics has been used mainly to treat conditions that affect the gut, such as diarrhea, ulcerative colitis, and intestinal inflammation.

Despite this, recent evidence has revealed how probiotics can also improve mental conditions, redefining the importance of gut-bacteria. In 2013, a Cal-Tech study concluded that mice whose intestines were injected with Bacteroides fragilis had reduced psychological symptoms of anxiety and depression. One possible mechanism for this profound effect is a chemical signal sent through the vagus nerve – a large nerve which connects the brain to organs such as the heart, lungs, and intestines. For example, one experiment found that ingestion of the bacterium Lactobacillus rhamnosus stimulates the vagus nerve in the gut of mice, changing the synthesis of receptors for the neurotransmitter -aminobutyric acid (GABA) in the brain, reducing anxiety.

Another way that probiotics may improve mental health is by reducing the leakage of the gastrointestinal (GI) tract. The GI tract is made up of the tubing from the mouth to large intestine. It absorbs nutrients from food for our bodies to metabolize. Certain conditions can make the lining of the GI tract leaky, resulting in the absorption of fewer nutrients. Injecting Bacteroides fragilis into mice with autistic symptoms reduces the leakiness of the GI tract, allowing essential nutrients to be absorbed that ameliorate some psychological symptoms of the autism.

Moreover, B. fragilis is not the only bacterium that has been shown to have beneficial effects for mental health. Another 2013 study demonstrated that in children with autistic symptoms, intestinal cultures had lower levels of certain bacterium genera such as Coprococcus, Prevotella and unclassified Veillonellaceae. Yet another study found that ingesting the strains Lactobacillus helveticus and Bifidobacterium longum improved symptoms of depression and stress in human volunteers.

This research is opening the door for a new wave of mental health treatments. A genetically modified bacterium strain that possesses multiple genes linked to mental health could be used as an alternative to artificially synthesized drugs. The potential for a natural organism that produces beneficial metabolites within the body itself is promising. Additionally, prescribing certain amounts of probiotic pills to patients would allow for easy regulation of these effects. However, research into the psychological abilities of probiotics – which doctors have appropriately dubbed “psychobiotics” – is still scarce.
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On November 19th of 2014, researchers presented the new evidence for the link between gut-bacteria and the brain at the annual Society for Neuroscience meeting in a symposium called “Gut Microbes and the Brain: Paradigm Shift in Neuroscience.” Hopefully, this wave of recent findings will stimulate further research into the ability of bacterium to influence mental health. In the near future, advanced probiotics may be involved in treating intestinal, immune and psychological conditions, and one day a simple ingestion of bacterium-infused food may replace the abundant need for synthetic antidepressants or other psychiatric drugs. But until then, keep eating Greek yogurt – your brain may thank you later down the road.