Time was, “sport drink” meant one product: Gatorade. Today, that original yellow thirst quencher with a boost—added electrolytes—is just one among a rainbow of sport drink options, each with “specially formulated” recipes—one for hydration, another for energy. And just when it seemed the market had peaked, the game changed. New performance beverages sell themselves on what they leave out—processed nutrients and artificial sweeteners—rather than what they add. By Madeline Senkosky