Novak Djokovic's recent winning streak stunned tennis commentators, leaving them wondering, "What's this guy on?" The better question is: What is he not consuming? The answer: pasta, bread and other foods containing the wheat protein gluten. Djokovic credits his good-to-great transformation to his recent diet change, saying that he "feels sharper and [has] lost a few pounds." He made the switch last year after his nutritionist determined he was allergic to gluten.