You just polished off a bowl of mint chocolate chip, and suddenly you’re craving a drink. Sound familiar? Post-dessert thirst is a common reaction—but why is it that sweet treats make us feel so parched?

To find out, we called Caroline Apovian, MD, a professor in the endocrinology, diabetes, and nutrition department at the Boston University School of Medicine. The reason has to do with a spike in your blood sugar levels, she says: “When you put sugar in your system, it first goes to your stomach, and then into your bloodstream.”

Once the sugar particles reach your blood, water moves out of your cells and into your blood, to restore balance in your blood. As your cells lose water, they send signals to the brain indicating that they need more H2O. The result? You feel the urge to sip on something.

“This [chain of events] happens pretty quickly,” sat Dr. Apovian. “Since glucose is absorbed by the gut and into the bloodstream fairly fast, you might feel thirsty within 5 or 10 minutes.” (Any thirst you feel immediately after noshing is likely induced by the act of eating itself, she points out, and not a change in your blood sugar.)

The best way to quench sugar-induced thirst is with a glass of good ol’ H2O, says Dr. Apovian, even though you may be craving something sweeter, like juice, lemonade, or hot cocoa. Having a sugary beverage on top of dessert won’t do you any good, she explains: “You’re not only confusing your energy balance system by putting more sugar into your body, but also getting a load of empty calories.”