When workouts leave you drenched, or when it's so hot outside that your clothes cling to your body like Saran wrap, start drinking. If you don't rehydrate, your body and brain can suffer; mild dehydration can tank your mood, concentration and energy levels. But not all fluids are created equal—and water isn't always the best beverage for the job. “When we drink, fluids are not available to the body immediately but take some time to be absorbed from the gut into the bloodstream,” says Bridget Benelam, a public health researcher with the British Nutrition Foundation. How fast this happens is determined, in part, by what's in the fluid.
