“Every study we’ve done has shown that fat people have a different set of microbes than thin people,” says Tim Spector, a genetic epidemiologist and the author of The Diet Myth: Why the Secret to Health and Weight Loss Is Already in Your Gut.

This discrepancy is a relatively new discovery. For decades, scientists’ ability to study the microbiome was limited because the vast majority of bacterial strains aren’t easily cultivated in a lab. Spurred by the advent of third-generation DNA sequencing technology in the mid-1990s, which enabled the quick, cheap identification of microbe strains via their genetic code, there’s been a renaissance in bacteria-focused studies.

Researchers have already uncovered some interesting results, connecting changes in gut bacteria composition to shifts in immune, metabolic and behavioral states. Read the full story on how gut bacteria, antibiotics and weight gain may all be connected.