Swimming superstar Michael Phelps once claimed he scoffed up to 12,000 calories a day. Usain Bolt's big sprint rival Yohan Blake says he chomps 16 ripe bananas every 24 hours.

A tiny Japanese athlete easily tucked away 50 pieces of sushi after training, while another marathon runner gobbled plates of raw mince.

Or how about the weightlifter who drinks the first milk of a cow that has just given birth?

With extreme eating habits like these, it may be some surprise to learn that within the Olympic Village there lurks a culinary trap that can potentially tip athletes over the fine line between success and failure at London 2012.

Competitors spend years honing their bodies to perfection, scrupulously eating the right foods, avoiding the wrong ones ... and then?

They encounter the Olympic Dining Hall.

With a McDonald's at one end and machines dispensing other sponsors' soft drinks and confectionery, the giant eating area provides mountains of fodder from around the world -- a full gamut of gluttony from one extreme of the health spectrum to the other.

It's a 5,000-capacity, 24-hour facility where organizers expect 25,000 loaves of bread, 232 tons of potatoes, 75,000 liters of milk and more than 330 tons of fruit and vegetables to be consumed by the time the Games finish on August 12.

Some 1.2 million meals will be served -- 60,000 a day.

"For the younger athletes it's an exciting new experience," says sports scientist Jess Corones, who works with the Australian Olympic swim team.

"It's all free. There's thousands of athletes and there's pretty much every kind of cuisine that you could possibly want. There's a stand that gives you unlimited McDonald's, there's machines that pump out unlimited amounts of soft drinks for you.

"That's exciting and it can be a distraction for them. They think, 'Oh this is so cool,' and they just run to it -- but you have to remind them that it'll still be there when they've finished competing and that until they've finished competing they've got to stay on their normal routine."

What passes for "normal" can vary wildly.

Phelps, after winning a record eight gold medals at Beijing 2008, told NBC that he gorged on carbohydrate-heavy pasta and pizza at the height of his extreme training. Jamaica's 100-meter world champion Blake says he eats so many bananas to keep up his potassium levels.

British weightlifter Jake Oliver says that every morning he drinks a shake containing colostrum -- a protein-rich form of milk produced during the late stages of cows' pregnancy. "I've tried to get people to try it, but they won't. Just the smell of it is enough to put people off," he told UK newspaper The Guardian.

Or even Japan's former Olympic marathon champion Naoko Takahashi, a diminutive runner who told CNN she could consume about 2 kg of fish after a big session.

"I only ate twice a day. But I ate a lot," said Takahashi, who won gold at Sydney 2000 and now works in television.

However, it's rare for athletes to eat quite that much, says Corones, who first worked with Australia's track and field team at the 2004 Athens Games. Phelps actually admitted this year that the report of his gargantuan appetite was a myth, saying such intake would be impossible.

"I find it hard to believe," Corones said. "I tell you what, if he is eating that he's got a pretty exceptional metabolism! The only people that I've seen eat close to that are the hammer throwers, and they all weigh in at 120 kilos."

Corones has had some experience of quirky diets though, citing Australia's Ethiopia-born marathon runner Sisay Bezabeh from the 2004 team.

"We had our camp in Italy and all he used to eat every dinner was a bowl of raw mince. I found it quite disgusting but he needed iron for his running, and that's what he did. You wouldn't get many athletes doing that these days."

Good nutrition from a young age can be vital if you want to be an elite athlete.

Becky Stevenson, a British dietitian based in the Netherlands, has researched the importance of vitamin D for improving performance and avoiding injury.

She cites reports that showed Chinese adolescent girls with adequate vitamin D had "significant higher bone mass and muscle strength." Questions have been raised about teenage swimmer Ye Shiwen's incredible performances at London 2012, but such research has yet to prove that high levels of vitamin D could be a contributing factor to her success.

"We know low levels may impact muscle strength and bone turnover, but if an athlete has adequate levels there is no evidence of an enhanced benefit to performance, so natural talent and athletic ability is more likely," Stevenson told CNN.