As Novak Djokovic climbed from a distant No. 3 to a convincing No. 1 in men's tennis over the past few years, he gave a lot of credit to a new gluten-free diet. He was also famously outed by this newspaper during the 2011 U.S. Open for his devotion to the benefits of sitting inside a pressurized egg-shaped contraption called a CVAC.

But in a new book that will be released next month, Djokovic reveals much more about the diet and regimen he follows—details he has, until now, kept quiet.

...