Novak Djokovic has become the world's top tennis player since overhauling his diet in 2010. "I observed him playing in the Australian Open," says the Serbian's former nutritionist Dr. Igor Cetojevic. "The commentator repeatedly referred to 'his asthma' and the problems he had breathing."
(CNN) -- The lactic acid builds up, your muscles are screaming, your body temperature sky-rockets -- trying to stay two shots ahead of your opponent proves impossible as your thoughts fragment into near delirium.
Five hours charging around a tennis court can be sheer hell even when you're winning, but if your body is out of balance then it's an even harder challenge.
Sunday's Australian Open finalists Novak Djokovic and Andy Murray once struggled with their fitness, but both have transformed their tennis careers since discovering a diet secret that is battling for acceptance in the world of mainstream sports science.
The benefits of going gluten free have been extolled for years by alternative health practitioners, but they have been brought to wider attention due to the exploits of high-profile stars such as Djokovic, whose wheat intolerance caused the world No. 1 severe breathing problems.
Read: The destiny of family guy Djokovic
"I knew from my experience that asthma was not the boy's problem but rather it was reflecting a symptom of something that was going on with his digestion," says Dr. Igor Cetojevic, who worked with Djokovic for a year up until his Wimbledon triumph in 2011.
"It was his sensitivity to gluten that was compromising his lungs," he adds, citing that in Chinese medicine there's believed to be a relationship between the large intestines and the lungs.
Our diet has changed dramatically in the past century, especially in Western countries. It's a trend that's spreading around the world due to the globalization of commerce, and the food industry in particular.
"I believe one of the problems is over consumption of gluten-containing grains, especially wheat, and the fact that it is genetically different from ancient wheat," says naturopathic physician Hamish Everard.
Cutting out wheat-based foods such as bread and pasta could be the best thing you ever do, says one of his clients, tennis coach Pete McCraw, who has helped develop top players such as Maria Sharapova and Jelena Jankovic.
Read: Djokovic beats Murray in Melbourne final
"The energy level that you have is something I've never experienced before. You don't ever have that crash, the high and then the low," McCraw told CNN.
"Those periods of the day when you crave carbs or sugar, feeling drowsy at work or in the car or wherever, you don't have that anymore, it's a completely different thing -- it's sustained, you don't have the foods cravings like I used to.
"It's a completely different energy source that your body's operating from. The ability to maintain a lean athletic figure is effortless."
The problem is not just wheat, but also processed dairy and sugars -- all of which we consume more regularly and in higher quantities than ever before.
"The gluten in food produces certain conditions; dairy, especially when produced conventionally, contributes to other factors to the detriment of our health," says Cetojevic, who is trained in both conventional and alternative medicine.
"Generally, milk is for babies. We don't need dairy products as we get older," he adds, and also warned against the intake of processed sugar.
"The change in food production has increased yields to the point of surplus but has not improved the quality of the food we eat. Often it contains traces of pesticides, hormones, preservatives, artificial colors, flavor enhancers and I won't even begin to talk about genetically modified organisms."
Read: Australian Open men's final as it happened
About 18 months ago, McCraw started noticing symptoms of extreme lethargy in young players he was working with.
"They were presenting chronic fatigue symptoms, although they weren't diagnosed in a traditional way, in terms of blood markers -- everything would come back reasonably normal," he said.
"Athletes would be complaining of excessive tiredness, even after light sessions. During a normal daily activity it was fine but then as soon as they began to exercise their blood sugar levels would drop significantly, and that causes concentration-behavior issues, (problems with) focus, emotional control.
Novak Djokovic of Serbia celebrates winning the men's singles final match against Andy Murray of Great Britain at the Australian Open in Melbourne on Sunday, January 27. Djokovic won 6-7 (2), 7-6 (3), 6-3, 6-2.
However, Cetojevic said the problem was Djokovic's intolerance to gluten -- which is found in grains such as wheat and their byproducts -- so he had to eliminate it from his diet and add more fruit, rice, vegetables and fish protein. The Serbian has now won a record three successive Australian Open titles.
This image, provided by Australian naturopathic physician Hamish Everard, shows what blood looks like before going on a gluten-free diet. The cells are clumped closely together.
This image, taken after the subject went on a gluten-free diet, shows the blood cells are able to flow more freely -- allowing better transportation of oxygen around the body.
"After eliminating grains from the patients' diet, all of their symptoms began to resolve within only a few days," says Everard. "Not only did their gastrointestinal symptoms disappear, but so too did other metabolic symptoms such as chronic and general fatigue, diabetes (high and low blood sugar), high cholesterol, decrease in inflammatory markers, soft tissue injuries, joint pain and stiffness, improved cognition (concentration), less anxiety, decreased depression, increase in bone density in osteoporosis patients, eczema, psoriasis and a decrease in acidity levels."
Experts say many health problems stem from changes in food production. "The hybridization of the native European wheat with a shorter, hardier strain from South America in the 1940s produced the particular gluten protein that triggers the sensitivity in people's digestive system," says Cetojevic. "For thousands of years people ate and digested wheat without adverse effects, but we haven't yet adapted to the new protein in the hybrid variety that is now widely grown and marketed for its convenience and higher yield. People are better off eating the older strains such as spelt and kamut."
Pasta is another staple food for many athletes. "Educating people on long-term dietary habits often depends upon how bad they felt before," says Everard. "The worse you were, the more willing you are to make the change. Athletes are disciplined and often do whatever is required of them to improve physically, mentally and emotionally for their sport. I try to teach the 80/20 principle: 80% good 20% bad. Once the underlying causes of gluten intolerance has been corrected, most patients can consume it again in some form or another."
People who are gluten intolerant suffer damage to their intestinal microvilli. "We have seen a definite link in gluten intolerant patients as far as a decrease in beneficial stomach bacteria, an increase in acidity and a decrease in both gastric digestive enzymes and pancreatic enzymes," says Everard.
Cetojevic believes the trend towards gluten-free diets is growing. "In 2011 I saw that most of the players' lounges on the tennis circuit offered gluten-free options, which was not the case in 2010," he says. "I observed that some of the top players have slimmed down and are faster on the court."
Djokovic holds the Norman Brookes Challenge Cup on January 27.
Djokovic hits a return against Murray on January 27.
Djokovic plays a backhand on January 27.
Murray plays a backhand against Djokovic on January 27.
Djokovic serves to Murray at Melbourne Park on January 27.
Murray reacts to a point on January 27.
Murray wipes his face during his men's final match against Djokovic on January 27.
Murray receives medical attention to his foot on January 27.
Crowds cheer during the men's singles final match on January 27.
Djokovic plays a forehand on January 27.
Djokovic plays a smash forehand on January 27.
Murray plays a backhand on January 27.
Murray plays a backhand against Djokovic on January 27.
Four-time Australian Open men's singles champion Andre Agassi carries the Norman Brookes Challenge Cup before the men's final match on January 27.
Murray plays a forehand on January 27.
Victoria Azarenka of Belarus poses with the winner's trophy after defending her Australian Open title on Saturday, January 26. Azarenka defeated Na Li of China 4-6, 6-4, 6-3.
Victoria Azarenka of Belarus celebrates winning her women's final match.
Li Na plays a forehand in her women's final match against Belarus Azarenka.
Belarus Azarenka hits a return during the women's final, which she won 4-6 6-4 6-3.
Li Na falls for the second time during her women's final match.
Benlarus Azarenka reaches for a forehand during Saturday's final.
Li Na rips a forehand Saturday. Li was also a finalist in the 2011 Australian Open.
Belarus Azarenka, who retained her world No. 1 ranking, serves in Saturday's final.
Mike Bryan, left, and his brother, Bob Bryan, of the U.S. celebrate after their victory over the Netherlands' Robin Haase and Igor Sibling during the men's doubles final January 26.
Robin Haase plays a forehand in Saturday's doubles match against the Bryan brothers.
Bob Bryan reaches for an overhead in the men's doubles final.
Nick Kyrgios of Australia serves in his junior boys' final match against Thanasi Kokkinakis of Australia on January 26. Kyrgios captured the boys singles title in straight sets.
Stephane Houdet of France plays a forehand in his men's wheelchair singles final match on January 26 against Shingo Kunieda of Japan. Kunieda won 6-2 6-0.
Sabine Ellerbrock of Germany plays a backhand in her wheelchair singles final against Aniek Van Koot of the Netherlands on January 26. Van Koot took the title with a 6-1 1-6 7-5 victory.
Katerina Siniakova of the Czech Republic plays a forehand in her junior girls' final match against Ana Konjuh of Croatia on Saturday. Konjuh won the championship 6-4 6-4.
Andy Murray of Great Britain plays a backhand in his semifinal match against Roger Federer of Switzerland on January 25. Murray defeated Federer 6-4, 6-7 (5-7), 6-3, 6-7 (2-7), 6-2.
Ashley Barty of Australia, right, watches as compatriot Casey Dellacqua plays a return during their women's doubles final against Sara Errani and Roberta Vinci of Italy on day 12 of the Australian Open in Melbourne on Friday, January 25. The Italian pair beat Barty and Dellacqua 6-2, 3-6, 6-2.
Na Li of China pauses during a news conference on January 25.
Sara Errani and Roberta Vinci of Italy celebrate winning their final doubles match against Ashleigh Barty and Casey Dellacqua of Australia on January 25.
A supporter of Britain's Andy Murray watches during his men's singles semifinal match against Switzerland's Roger Federer on January 25.
Andy Murray of Great Britain plays a backhand on January 25.
Roger Federer of Switzerland plays a backhand on January 25.
Italy's Roberta Vinci, left, and Sara Errani pose with the winner's trophy after their victory over Australia's Ashleigh Barty and Casey Dellacqua on January 25.
Andy Murray of Great Britain takes a breather in his semifinal match against Roger Federer of Switzerland on January 25.
Andy Murray of Great Britain and Roger Federer of Switzerland play their semifinal match in Rod Laver Arena on January 25.
Roger Federer of Switzerland plays a semifinal match against Andy Murray of Great Britain on January 25.
Roger Federer hits a return on January 25.
Andy Murray of Great Britain plays a forehand on January 25.
Novak Djokovic of Serbia celebrates winning his semifinal match against David Ferrer of Spain during the Australian Open in Melbourne on Thursday, January 24. Djokovic won 6-2, 6-2, 6-1.
Djokovic signs autographs for fans on January 24.
Sloane Stephens of the U.S. reacts during her women's singles semifinal match against Victoria Azarenka of Belarus on January 24. Azarenka won 6-1, 6-4.
Na Li of China plays a forehand in her semifinal match against Maria Sharapova of Russia on January 24. Li won 6-2, 6-2.
A tennis fan sits in the stands during Day 11 of the Australian Open at Melbourne Park on January 24.
Li plays a forehand on January 24.
Sharapova plays a return against Li on January 24.
Ferrer plays a backhand on January 24.
Stephens plays a return against Azarenka on January 24.
Djokovic reacts after a point against Ferrer on January 24.
Fans watch the men's semifinal match between Ferrer and Djokovic on January 24.
Azarenka plays a forehand against Stephens on January 24.
Brothers Bob, left, and Mike Bryan battle Simone Bolelli and Fabio Fognini of Italy in a doubles semifinal match on January 24. The brothers won 6-4, 4-6, 6-1.
Stephens plays a return on January 24.
Ferrer plays a backhand against Djokovic on January 24.
Djokovic plays a backhand against Ferrer on January 24.
Stephens pauses during her match against Azarenka on January 24.
Sloane Stephens of the U.S. celebrates after beating compatriot Serena Williams, who was favored to win the tournament, during their women's singles match on Day 10 of the 2013 Australian Open in Melbourne on Wednesday, January 23. Stephens won 3-6, 7-5, 6-4.
Stephens plays a backhand in her quarterfinal match against Williams on January 23.
Williams stares down the ball during her match on January 23 against Stephens.
Williams broke her racket while playing Stephens on January 23.
Williams stretches across the court on January 23.
Italy's Sara Errani plays a backhand in her women's doubles quarterfinal match with compatriot Roberta Vinci against Ekaterina Makarova and Elena Vesnina of Russia on January 23. Errani and Vinci won 6-2, 6-4.
France's Jeremy Chardy hits a return against Britain's Andy Murray during their men's singles match on January 23. Murray defeated Chardy 6-4, 6-1, 6-2.
Murray celebrates beating Chardy on January 23.
France's Jo-Wilfried Tsonga scoops up a return to Switzerland's Roger Federer during their men's singles match on January 23. Federer defeated Tsonga 7-6 (4), 4-6, 7-6 (4), 3-6, 6-3.
Federer plays a backhand to Tsonga on January 23.
Victoria Azarenka of Belarus hits a return against Russia's Svetlana Kuznetsova on January 23. Azarenka defeated Kuznetsova 7-5, 6-1.
Kuznetsova serves during her match against Azarenka on January 23.
Azarenka receives a towel during her match on January 23.
Novak Djokovic of Serbia stretches for the ball in his quarterfinal match against Tomas Berdych of the Czech Republic on Tuesday, January 22. Djokovic won 6-1, 4-6, 6-1, 6-4.
Fans watch Djokovic and Berdych play on January 22.
Berdych plays a backhand in his match against Djokovic on January 22.
Spain's David Ferrer watches the ball during his men's singles match against compatriot Nicolas Almagro on January 22. Ferrer defeated Almagro 4-6, 4-6, 7-5, 7-6 (4), 6-2.
Almagro reaches to smash the ball while playing Ferrer on January 22.
Na Li of China hits a return against Agnieszka Radwanska of Poland in their quarterfinal match on January 22. Li won 7-5, 6-3.
Radwanska stretches for a forehand while playing Li on January 22.
Li serves in her match against Radwanska on January 22.
Russian Maria Sharapova plays a forehand in her quarterfinal match against fellow Russian Ekaterina Makarova on January 22. Sharapova won 6-2, 6-2.
Makarova goes airborne in her match against Sharapova on January 22.
American Serena Williams hits a return against Russia's Maria Kirilenko during their women's singles match on Day Eight on Monday, January 21. Williams won 6-2, 6-0.
Kirilenko plays a backhand against Williams on January 21.
Jo-Wilfried Tsonga of France celebrates winning his fourth-round match against fellow French player Richard Gasquet on January 21. The final score was 6-4, 3-6, 6-3, 6-2.
American Sloane Stephens makes a return against Bojana Jovanovski of Serbia on January 21. Stephens defeated Jovanovski 6-1, 3-6, 7-5.
Bojana Jovanovski serves to Sloane Stephens on January 21.
Roger Federer of Switzerland serves in his fourth-round match against Canadian Milos Raonic on January 21. Federer won 6-4, 7-6(4), 6-2.
Svetlana Kuznetsova of Russia hits a backhand in her fourth-round match against Caroline Wozniacki of Denmark on January 21. Kuznetsova defeated Wozniacki 6-2, 2-6, 7-5.
A ball kid displays Australian Open tennis balls during a match on January 21 at Melbourne Park.
Jeremy Chardy of France serves in his fourth-round match against Italy's Andreas Seppi on January 21. Chardy defeated Seppi 5-7, 6-3, 6-2, 6-2.
Andreas Seppi plays a backhand against Jeremy Chardy on January 21.
Caroline Wozniacki of Denmark returns a backhand in her fourth-round match against Svetlana Kuznetsova of Russia on January 21. Kuznetsova won 6-2, 2-6, 7-5.
Caroline Wozniacki hits a return against Svetlana Kuznetsova on January 21.
Caroline Wozniacki serves in her January 21 match against Svetlana Kuznetsova.
Svetlana Kuznetsova shows off a tattoo on January 21.
Stanislas Wawrinka of Switzerland plays a return during his men's singles match against Serbian Novak Djokovic on Sunday, January 20, Day Seven of the Australian Open in Melbourne, Australia. Wawrinka lost 1-6, 7-5, 6-4, 6-7 (5), 12-10.
Djokovic celebrates his narrow victory January 20 against Wawrinka.
Spain's David Ferrer hits a return against Japan's Kei Nishikori during their men's singles match on January 20. Ferrer won 6-2, 6-1, 6-4.
Nishikori reacts during his match against Ferrer on January 20 as a ballgirl watches.
Ferrer plays a forehand against Nishikori on January 20.
Venus and Serena Williams of the U.S. are congratulated by Russian Nadia Petrova and Slovenian Katarina Srebotnik after winning their third-round doubles match on January 20.
Maria Sharapova of Russia serves in her fourth-round match against Kirsten Flipkens of Belgium on January 20. Sharapova defeated Flipkens 6-1, 6-0.
Sharapova serves in her fourth-round match against Flipkens.
German Julia Goerges, left, congratulates Na Li of China on winning their fourth-round match 7-6 (6), 6-1 on January 20.
Mike Bryan of the U.S. plays a forehand in his third-round doubles match with his twin, Bob Bryan, against Jeremy Chardy of France and Lukasz Kubot of Poland on January 20. The Bryans won 6-7 (4), 6-4, 6-3.
Serbia's Janko Tipsarevic looks at his wrapped foot during a break in his men's singles match against Spain's Nicolas Almagro on January 20. Almagro moved on to the next round after Tipsarevic pulled out of the match in the second set because of his injury.
Kevin Anderson of South Africa prepares to serve in his fourth-round match against Tomas Berdych of the Czech Republic on January 20. Berdych won 6-3, 6-2, 7-6 (13).
Huge crowds gather at Federation Square to watch Bernard Tomic of Australia play Roger Federer of Switzerland on Saturday, January 19. Federer won 6-4, 7-6 (5), 6-1.
Gael Monfils of France twists around to return the ball in his third-round match against compatriot Gilles Simon on Saturday, January 19. Simon defeated Monfils 6-4, 6-4, 4-6, 1-6, 8-6.
Britain's Andy Murray plays a forehand in his third-round match against Ricardas Berankis of Lithuania on January 19.
Maria Kirilenko of Russia celebrates match point in her third round match against Yanina Wickmayer of Belarus on January 19.
Andy Murray serves in his match against Berankis.
Juan Martin Del Potro of Argentina rests in between points in his third-round match against Jeremy Chardy of France.
Philipp Kohlschreiber of Germany serves in his third round match against Milos Raonic of Canada.
Maria Kirilenko of Russia serves in her third-round match against Yanina Wickmayer of Belgium on January 19.
Laura Robson of Britain plays a forehand in her third-round match against Sloane Stephens of the United States on January 19.
Serena Williams of the United States reacts in her third-round match against Ayumi Morita of Japan on January 19.
Maria Kirilenko of Russia plays a forehand in her third-round match against Yanina Wickmayer of Belarus.
Mansour Bahrami of Iran warms up for a doubles match on January 19. He and Wayne Ferreira of South Africa faced Australians Mark Woodforde and Todd Woodbridge.
Juan Martin Del Potro of Argentina serves in his third round match against Jeremy Chardy of France.
A ball kid throws a tennis ball in the third round match between Jeremy Chardy of France and Juan Martin Del Potro of Argentina.
Victoria Azarenka of Belarus plays a forehand in her third-round match against Jamie Hampton of the United States.
Ayumi Morita of Japan serves in her third round match against Serena Williams of the United States, on January 19. Williams won the match 6-1, 6-3.
Serena Williams of the United States plays a backhand in her third round match against Ayumi Morita of Japan, on January 19.
Bojana Jovanovski of Serbia signs autographs for fans after winning her third round match against Kimiko Date-Krumm of Japan, on January 19. The final match score was 6-2, 7-6, tie-breaker 7-3.
The racquets of Bob Bryan of the United States and Mike Bryan of the United States cross as they compete in their men's second round doubles match against Flavio Cipolla of Italy and Andreas Seppi of Italy on Friday, January 18. The Bryan brothers won 6-3, 6-4.
Novak Djokovic of Serbia serves against Radek Stepanek of the Czech Republic during their men's singles match on Day Five of the Australian Open in Melbourne, Australia, on Friday, January 18. Djokovic won 6-4, 6-3, 7-5.
Djokovic plays a forehand in his third-round match against Stepanek on January 18.
Tomas Berdych of the Czech Republic plays a backhand in his third round match against Jurgen Melzer of Austria on January 18. Berdych won 6-3, 6-2, 6-2.
Clouds loom over the stadium in Melbourne Park as Berdych and Melzer compete in their third-round match on January 18.
Stepanek reacts after a shot on January 18.
Ana Ivanovic of Serbia serves in her third-round match against Jelena Jankovic of Serbia on January 18. Ivanovic won 7-5, 6-3.
Maria Sharapova of Russia reacts after beating Venus Williams of the U.S. during their women's singles match on January 18. Sharapova won 6-1, 6-3.
Sorana Cirstea of Romania plays a forehand in her third-round match against Na Li of China on January 18. Li won 6-4, 6-1.
Alex Bolt of Australia plays a backhand in his third-round doubles match with Greg Jones of Australia against Daniele Bracciali of Italy and Lukas Dlouhy of Czech Republic on January 18. Bracciali and Dlouhy won 6-2, 7-6 (4).