Rafael Nadal thinks it is a passing fad and Caroline Wozniacki will not even try it on her pet dog, but Novak Djokovic is convinced that a gluten-free diet has been the key to his success.
Serve To Win, Djokovic's book about the diet that has transformed his health and his career, has been the talk of tennis since its publication last week, though the world No 1 does not appear to be making many converts. Djokovic says his health has improved markedly since he discovered his intolerance to gluten, a protein found in wheat.
"Oh no, I have extra gluten," Roger Federer joked when asked whether he had been tempted to follow the diet. "I've always paid attention to what I eat. I've always been a healthy eater. Clearly you can take it to the next step – when, to eat, exactly what, before the match, during the match, after the match, what to eat exactly if you're not sure.
"I grew up as a vegetarian when I was younger. I'm happy I can eat a bit of everything today, which makes it easier overall. I've seen some nutritionists from time to time, but nothing crazy or major."
Nadal also said a gluten-free diet was not for him. "I am happy with a normal diet," he said. "But I'm not saying it's a negative thing. Everybody is free to do what they want. Everybody does things differently."
Nevertheless, there was a hint of cynicism in Nadal's voice. "Now it seems like the gluten-free diet is great," he said. "After three or four years we will find another thing that will be great, too. Then the gluten-free diet will not work any more."
Djokovic said – with perhaps a hint of seriousness – that he had even put his pet dog, Pierre, on a gluten-free regime. "Pierre is following his daddy's diet, for sure," the Serb said. "That's why he's so fit."
However, Wozniacki, Djokovic's neighbour in Monte Carlo, said her dog Bruno would not be going gluten-free. "My dog is only having one life and I want him to enjoy it," she said. "Whether that means he's going to become a little bit chubby, then so be it. I'd rather have him a little bit chubby and happy than too skinny and miserable."
Djokovic insisted that he was not trying to convert anybody to the gluten-free cause. "The diet changed my life in a really positive way and affected positively my career and my overall feeling on and off the court," he said. "I particularly wanted to share this kind of food regime and this kind of change that affected my life positively with the people, just present them my own experience.
"I am not trying, through the book, to influence anybody's life or to tell people how they should eat or live or maybe treat their food. I'm just sharing my own experience and hoping that people who are reading it can actually take some valuable examples and experiences to implement in their own life.
"I've already got a few positive comments from random people. To hear that somebody felt positively after reading my book and made a positive change in their life is really nice to hear."