They say the way to the heart is through the stomach, but scientists are now saying it's the way to the mind too.
It's called the human microbiome: the billions of bacteria, fungi, and other microorganisms in your body.
Scientists at the University of California, San Diego Center for Microbiome Innovation say it is a new frontier in understanding human health.
"When we look at wellness and disease, focusing on the human aspect of the equation, we are missing 99 percent of the information that we should be looking at," said Dr. Sandrine Miller-Montgomery, Executive Director of the Center for Microbiome Innovation. "That's what microbiome scientists are doing."
Here's some food for thought: there are 100 million neurons in your guts, which is why hunger can affect your mood.
"You can have good memories associated with certain foods," said Lindsay Clark, a sophomore at UCSD. "And it can bring back comforting feelings.”
And that gut feeling that you've had before? That might have more logic than we once thought.
UCSD researchers are hopeful learning the secrets of these neurons in the stomach and intestines will lead to better cures for mental illness.
Scientists are learning one of the most important things when it comes to microbiome health is variety. That means eating a diet with fruits and vegetables that are all colors of the rainbow.
"The more diverse your gut microbiome is the likelier you are to be healthy," said Dr. Miller-Montgomery.
That's because there will be a more diverse range of good bacteria to fight off bad bacteria.
The emerging field will not only lead to better mental health and nutrition but possible new cures for diseases like cancer.
"In the future we can have companion treatments to oncology drugs where the person who was not responding because they did not have the proper microbiome could be a responder to the therapies," said Dr. Miller-Montgomery.