Muslims are required to abstain from food and drink from dawn to dusk during the 30-day month of Ramadan, which began Friday in most countries.
During long summer days in London, that translates into 18 hours of fasting - something that many Muslim athletes consider impossible to do without losing their competitive edge.
Many of the 3,500 or so Muslim athletes expected to compete at the London Olympics will keep eating as usual.
"I could not fast. I need all that stuff, like protein, carbs and minerals," Egyptian kayaker Mustafa Saied told The Associated Press. "I can do it after Ramadan and Allah will accept it because there was an important reason."
Some have looked for Islamic tenets that allow exemptions from fasting, such as for those traveling. Others decided to postpone fasting until after competitions, and some will compensate for the lost days with charity work or by donating to the poor.
"It's impossible for us to fast Ramadan during the London Olympics," said Yasser Hefny, an Egyptian modern pentathlete. "We have five disciplines to perform. We do a lot of effort during the whole day."
The High Egyptian Islamic Council gave athletes a reprieve by announcing a fatwa, or religious edict, stating that Olympic athletes are not required to fast during coaching or competition.
Egyptian pentathlon coach Sherif al-Eryan said athletes have also sought guidance from a cleric before traveling to London and had decided not to fast during the games. Like other athletes, al-Erayn said, they will have their "full menu in an open buffet" in the athletes village.
"I guess there is no problem. Our athletes could never achieve anything if they fasted this year," al-Eryan said. "They have religious permission for this. But it is necessary for them as Muslims to fast after the month of Ramadan for the days they had to eat during the Olympics."
However, the officials and coaches will be fasting "as we're not making as much effort as the athletes," al-Eryan added.
The Muslim lunar calendar moves back through the seasons, so Ramadan starts 11 days earlier each year under the Western calendar. The last time Ramadan started in mid-July was in 1980 during the Moscow Games.
Suleiman Nyambui of Tanzania was fasting and competing then. He won Olympic silver in the 5,000 meters.
"Once you decide to do something, Allah is behind you," Nyambui told the faith-based Religion News Service.
He said training during Ramadan is harder than competing, adding that the first days might be hardest for athletes who chose to fast because it takes the body some time to adjust.
"After that people are used to it," said Nyambui, who is now the secretary general of the Tanzanian Athletics Association. "People play soccer, they can go jogging, they can go swimming."
Many Muslim athletes have competed in professional or national competitions while observing the fast, including NBA stars Hakeem Olajuwon and Shareef Abdur-Rahim. Ramadan fell during last year's track and field world championships in South Korea, as well as during the 2010 Youth Olympics in Singapore.
For believers, Ramadan is meant to be a time of reflection and worship, abstaining from swearing, gossip and bursts of anger, remembering the hardships of others and being charitable.
London organizers said they are prepared to accommodate Muslim athletes, media, spectators, workforce and volunteers in all of London's Olympic venues. Teams can order fast-breaking packs which include water, energy bars and fruit. The athletes village dining hall offers 24-hour catering and halal meals.
"Ramadan is not just about abstaining from food and water, but also about improving ourselves as people and thinking of those less fortunate," said Younis Dhudwala, one of five Muslim chaplains in the Olympic Park, who was leading Friday prayers in the athletes village.
"Some athletes may find that fasting gives them inner strength and physical advantage to perform better and run faster," Dhudwala said. "We are here to support athletes in whatever they decide to do during the competition."
One interpretation of the Quran allows Muslims to break the fast if they are traveling, and many athletes - including most from the more traditional countries of the Gulf - qualify as travelers during the games.
"Our athletes will not be fasting during the Olympics," said Sheik Khalid bin Abdulla Al Khalifa, the chief executive of the Bahrain Olympic Committee. "It's simple in Islam. Since they are traveling, they can take these days at the Olympics on loan and then make up for them until next Ramadan."
French boxer Rachid Azzedine and British rower Mohammed Sbihi also said they would postpone fasting until after their Olympic competitions. After consulting with a cleric, Sbihi decided to donate 60 meals for every fast he will miss to poor people in Morocco, where his father is from.
There are no Muslim athletes on the U.S. team.
"It's really the athletes individual decision, but sporting performance is often not just about physical fitness, but also a matter of spiritual determination that may enable some to overcome higher obstacles," said Mohammed Abdelbari, a former secretary general of the Muslim Council of Britain, who has advised local organizers on Ramadan arrangements.
"What we are trying to do is to facilitate and accommodate all those athletes who decide to fast and compete during the Olympics."
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