What is the best drink for hydration? HINT: It isn’t water.

Normally, you assume that plain water would be your best go-to for staying hydrated. That’s why this research on hydration is so important, because it actually tests that idea we all thought was true.

Researchers from St. Andrews University in Scotland found that water earns about a B+ for quickly hydrating the body. But the surprising winners keeps you hydrated longer because they have more than just a couple of H’s and an O.

The lead scientist is Ronald Maughan, who pointed out that a drink’s nutrient composition matters a lot for the best hydrating drinks. For example, milk was actually the A+ best out of them all because it contains lactose, some protein, and some fat. These are important because they help to slow the emptying of fluid from the stomach and keep hydration happening over a longer period.

By the way, while we busting our long held assumptions here, what about coffee? I had always been told that coffee was a diuretic that takes fluid out of your body. Yeah, about that …  When it comes to coffee, “the dose makes the poison.” In other words, this study showed that your coffee is hydrating (or not) based on how much of it you drink. A normal 12-ounce coffee with about 80 milligrams of caffeine would be just as hydrating as water, according to Maughan’s research.

Of course, if you drink a lot (say, over 300mg of caffeine or about 3-4 cups, that could cause you to lose excess fluid through a short-term diuretic effect.