Religious requirements are a product of the culture they originated in. Christianity borrowed a lot from the Jews and the Romans. The Hebrews borrowed from wider Mesopotamian ideas. But times change, and rules that worked just fine hundreds of years ago sometimes become much more constricting today.
The London Olympics occurs during the fasting month of Ramadan for Muslims. Observant Muslims neither eat nor drink during daylight hours. That's problematic enough for people who eat several thousand calories a day, but even more-so in London, which has 17 hours of daylight right now. (It's only about 13 hours in Mecca, Saudi Arabia.)
Islamic religious scholars offer a variety of interpretations of the fasting rules. Some say breaking the fast is fine, as the Koran says people should not risk their health to fast. (Children, the elderly, pregnant women, and the seriously ill are also specifically exempt.) It is likely these people will fast after the Olympics and give alms to the poor to make up for not fasting now. Some countries, such as Egypt, have even issues religious edicts (fatwas) exempting Olympic athletes from the Ramadan fast.
Others say that while they can break their fast if they are truly starving, choosing to simply ignore the fast is a mark of arrogance, putting one's career before Allah. There are Muslims who are considering fasting through the Olympics, and simply consuming as many calories as possible during the 7 hours of night that London has.