For Jordanian marathon-runner Methkal Abu Drais, the timing could not be worse. Not only is he preparing for one of the races of his life, he's doing it during Ramadan, the Muslim fasting month.
"I tried after I arrived in London to train while I was fasting but I realised it is very, very difficult because I'm taking part in a race that needs a lot of energy," he told AFP. "I think I will reverse my decision to fast."
It's a dilemma faced by about 3,500 Muslim athletes at London 2012, which coincides with a time of year when they would normally forgo food, drink and sex between dawn and dusk.
Most Muslim countries have given their athletes special dispensation to postpone Ramadan during the Games, to help them maintain their strength, and fast when they return home.
But many competitors are still insisting on observing Ramadan, one of the most spiritual periods in the Islamic calendar when fasting is usually seen as compulsory.
Morocco's men's football team have pledged to fast during the Olympics despite a request from their Dutch coach Pim Verbeek.
"We must fast because this is an obligation and I think that God will help us on the day of the games," said Morocco's Atletico Madrid-bound goalkeeper, Yassine Bounou.
"We're used to playing in Ramadan and it won't negatively impact us."
In judo, the UAE's Hamid Alderei is training only after breaking his fast, but among Niger's six-strong team, Zakari Gourouza is the sole athlete not observing Ramadan.
"The other five will fast because they're here just to take part. They're not likely to win any medals and fasting is a priority for us," explained Niger rower Hamadou Djibo Issaka.
Moroccan boxing coach Abdel Haq Achic said he found it difficult to persuade his athletes not to fast despite the significant impact on their strength, energy and weight.
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"Boxing is very tough and as we need to train twice a day the athletes can't do it. They lose a lot of their energy so they must eat to have good preparation for competition. We spoke to all the athletes and we told them they need to eat to be fit for the competition.
"After three hours of talking with them they decided not to fast. It was difficult for them to accept this decision because they are practising Muslims, but there's no other solution if they want to compete for medals."
According to the provisions of the Koran, Muslims can be excused fasting if they are sick or travelling, meaning athletes visiting London can postpone the ritual without guilt.
Some delegations consulted clerics before travelling to London; others even tried to change the dates of Ramadan to avoid clashing with the Games.
"The delegation met the mufti before coming to London. He told them that you are travelling and God will facilitate everything for you," said Egypt team official Aladdin Jabar.
"He gave them permission to eat. And now everything is up to the athletes."
Hassan Rifaat, general coordinator for the UAE, said each of the team's athletes had been left to make their own decision about fasting.
"There are some athletes fasting and there are others who eat. There's no official instruction from the Emirates Olympic Committee on that," he said.
"Every athlete does what he's comfortable with. It depends on his condition."
Egypt's first ever Olympic sailor, Ahmed Habash, has eased the problem by fasting according to sunset in his home country, meaning he can eat from 7:00 pm.
"In Egypt sunset is 7:00 pm and here in England it is 9:00 pm. During the actual races I'm not going to fast," he said. "It does mean when I return home I'll have to re-fast, but only for the five days I miss."
Muslim competitors have also been provided with prayer books, a quiet room and halal food in the Olympic village.
"They know that it is Ramadan and they are totally prepared for it. They have even sourced halal food and they have planned every meal for meal for me," Habash said. "I cannot believe it. I'm so happy to be here."