Maybe you’re the type that swears by coffee—you can barely open your eyes before you’ve had a cup. Or perhaps you feel jittery after sipping on anything caffeinated. Turns out the two groups are genetically different, and it all has to do with how quickly you metabolize caffeine. If you break it down fast, you get clean bursts of energy that keep you alert.

On the other hand, slow metabolizers often find coffee gives them the jitters and makes it hard to fall asleep. Short of a DNA test, there’s no way to determine whether your parents passed along the coffee-lover’s gene, but most of us can probably guess which camp we’re in.

(h/t The New York Times)