How did Novak Djokovic conquer the tennis world?

Maybe the answer is as simple as this: Since last year, he's swearing off pasta, pizza, beer, French bread, Corn Flakes, pretzels, empanadas, Mallomars and Twizzlers—anything with gluten.

It's no secret that Djokovic has had a breakout season, or that he has been, by any reasonable standard,...