Gut bacteria are believed to greatly influence one’s health, from appetite and weight loss to mood and emotions. Now, new research highlights how certain kinds of these beneficial bacteria can optimize the immune system and reduce stroke’s severity.

Stroke remains the second leading cause of death around the world.

The human gut, on the other hand, is considered the “second brain,” where the walls of the digestive system contain microbes that could form brain structure and potentially influence behavior, mood, and even the development of diseases such as Alzheimer’s.

In a new study, researchers from Cornell University gave mice a number of antibiotics and induced ischemic stroke, the most common kind of the condition, two weeks after. In ischemic stroke, an obstructed blood vessel hinders blood from getting to the brain.

Findings showed that antibiotic-treated mice experience a stroke that was around 60 percent less severe than those who did not receive the drug treatment. Their gut microbiota directed immune cells in the gut to shield the brain from the full force of the stroke.

For study author and neuroscience professor Dr. Josef Anrather, the results demonstrated a new link between the human brain and intestinal environment.

"The intestinal microbiota shape stroke outcome, which will impact how the medical community views stroke and defines stroke risk,” he says.

It remains unclear which bacteria provided the benefits, but it has been established that they did not chemically interact with the brain. Instead, these bacteria influenced neural activity through altering the action of gut immune cells, which went to meninges or outer brain coverings and organized a stroke response there.

In addition, it appeared that the subjects’ immune system decreased the impact of strokes through formulating a response outside the brain itself. Co-author Dr. Costantino Iadecola likened it to a conductor “who doesn’t play an instrument himself” but instead instructs different orchestra players on how to create music.

This discovery makes dietary changes a promising way to prevent future strokes, especially among those who are most at-risk. Adjusting one’s diet – which has the biggest influence on gut microbiota – is much easier to do than undergo medication, added Anrather.

The findings were published March 28 in the Nature Medicine journal.

The human body is believed to contain 100 trillion microbes, or 10 times more bacteria than total cells in the body. Good bacteria are constantly at war with harmful ones, where an imbalance leads to dysbiosis, which has been associated with a number of disorders.

Learn more about microbes and mental health in this LabRoots infographic.