People who suffer from anxiety may take antidepressants or another medicine to treat their brain.
But a new study suggests gut bacteria actually plays a major role in anxious feelings.
A team of scientists discovered that certain gene regulators in the brain - called microRNAs - play a key roll in anxiety-type illness and behaviour and are affected by bacteria levels in the gut.
This study, done by the University of Cork, is one in a growing body of data on gut bacteria and physical and mental health.
Pharmaceutical and wellness companies have noticed, and have been marketing probiotics said to improve general physical and mental health for years already, as we reported in January of 2014.
It's unclear, though, if the gut is influencing the brain and its development, or if the brain is influencing the gut.