For decades, the "fun fact" circulated that bacteria outnumber human cells 10-to-1 in our bodies. In 2016, researchers at the Weizmann Institute finally did the math properly—and the truth is both less dramatic and somehow weirder.

The average human body contains about 30 trillion human cells and 39 trillion bacteria. That's roughly 1.3 bacteria per human cell, making you about 43% human by cell count. The numbers are so close that the researchers noted, with perfect scientific deadpan: "Each defecation event may flip the ratio to favor human cells over bacteria."

Most of those 39 trillion bacteria live in your colon. They're part of your microbiome—the community of microorganisms that helps digest food, train your immune system, and even influence your mood. You're not just you. You're a walking ecosystem.