We often hear about "good bacteria."

The stuff in your gut that actually helps you fight off viruses and regulate your system.

The terms "probiotic" and "*prebiotic" are also making the rounds.

Researchers at the University of Colorado Boulder just wrapped up a first-of-its-kind study about what probiotics and prebiotics actually do for you.

9NEWS spoke with medical expert Doctor John Torres. He helped explain the difference.

"You talk about good bacteria that's the probiotic part of this equation, the good bacteria the probiotic that lives in our gut, does all sorts of things for our body and we're learning more and more just how important they are and just how important it is to keep that good bacteria in check," said Dr. Torres. "That bacteria helps with cardiac health, it helps with mental health functions, it helps with our overall body health, but the good bacteria also needs something to live on - those are the prebiotics."

Dr. Torres explained further where prebiotics are found.

"Those are not bacteria, but those are food that bacteria lives on. Those mostly come from fiber type foods that we eat in our diet," he said.

The CU Boulder study says dietary prebiotics can improve sleep and help with stress.

"They (reasearchers) looked at rats, but there is no reason to think it doesn't work on humans as well although future studies will tell if that happens. They basically gave these rats prebiotics what we were talking about the fibrous, or the chocolate type foods, to help the probiotics thrive. They found out when they got the prebiotics they were able to sleep better in two different types of sleep cycles what we call non-REM, which is our restorative get our bodies and minds back in tune, and REM sleep which actually helps when we're undergoing stressful situations," Dr. Torres said.

There are several foods rich in prebiotics. Dr. John says chicory root is one of the best, but you can also apples, bananas, garlic, onions, and even chocolate.

He noted moderation is key, especially with chocolate, because of the sugars and calories in a lot of foods.