(CNN) — You’ve probably heard that expression “you are what you eat.”

There’s a lot more truth to it than you may think, due to the 100 trillion microbes that make up your microbiome: a combination of fungi, bacteria and viruses that resides in your gut, primarily in the large intestine.

Researchers estimate the total surface area of the human gut at 3,000 square feet — larger than a tennis court — with the number of microbes in it outnumbering human cells 10 to one.

Though words like “bacteria” and “fungi” might commonly be associated with infections or disease, the ones found in the microbiome are the peacekeepers of your body, helping digest food, fight disease and regulate the immune system.

Today, researchers at the Center for Microbiome Innovation at the University of California, San Diego are trying to map and understand this crucial component of our health through the American Gut project — a slight misnomer, as the project has collected over 10,000 samples from more than 43 countries.