What the hell is this hydration index?
Researchers wanted to find out how much water your body absorbs from various drinks, based on several factors: how many carbs and electrolytes are in each drink, the sodium content, and if there’s a diuretic present.
The hydration index attempts to recreate with liquids what the glycemic index does for food, but somewhere along the way the ranking ends up claiming beer is basically on par with sports drinks at replenishing lost fluids. Which is totally fine!
Researchers also looked at how much each person peed after drinking each beverage, and compared it to the still water control group. Full-fat milk, for example, created less urine than water did in participants, but coffee produced more -- not shocking to anyone who's had to sit in traffic after chugging a venti iced coffee.
By the study’s standards, less urine equated to more hydration. To put it into chart form, researchers divided the amount of urine passed after drinking the still water, by the pee passed after each test beverage, creating a "beverage hydration index," or BHI. A high BHI means more water is retained in the body than if the drinker had consumed an equal volume of still water. They also left a margin of error to include the water content of each beverage (water obviously has more water content than coffee does, for example), but that didn’t seem to make much of a difference.