It was a ham and cheese sandwich that proved my undoing. Perhaps it is a little unfair to place all of the blame on one sandwich for it was not acting alone. They were a gang of two: sliced corner to corner they bulged with their filling, leering horribly with white bread lips. I think by that point I had begun hallucinating.

Perhaps the sandwiches were less to blame than the awful prospect of what came after: a half-kilogramme of pasta. The situation was hopeless. I had waited until late afternoon, and still I could not eat lunch.

So ended my day on the Michael Phelps diet, a regime that, if followed rigorously, will either transform you into the finest Olympian of your generation, or render you critically obese. It is hard to describe the hours that followed my surrender with any delicacy: I will only say that I had a lot of time to myself in a very small cubicle to think about what had gone wrong.

Earlier this week, as the American swimmer hauled himself, with eerie regularity, onto a gold medal podium in Beijing, the details of this peculiar 12,000 calorie daily diet had emerged. It appeared to be the secret of his success. The specifics of it were all laid out as clear as any weight-watchers plan. All that was needed was a little determination, and one could eat ones way into a professional swimming career. Of course it would also be necessary to swim six hours each day, fifty miles a week, but get the diet right, it seemed, and the Olympic swimming would follow.

In the lobby of the Beijing Intercontinental Hotel, a stones throw from the National Aquatics Centre, I explained my requirements to a charming receptionist. “I wish to eat like Michael Phelps in your restaurant,” I said.

“Michael Phelps?” she said.

“You know, the swimmer. I want to eat the same lunch as Michael Phelps eats, tomorrow, in your restaurant. I was wondering if-”

“Michael Phelps?” she said. “He is coming here for lunch!”

“No, no, hang on. I’m coming here for lunch. Not Michael Phelps.”

“Oh,” she said. “I see.” She was devastated.

Vicente, the manager of the hotel’s restaurant, cleared the prospective lunch menu – 500g of pasta, two large ham and cheese sandwiches – with the chef. Then I booked breakfast at an American-style café in downtown Beijing.

The manager there nodded thoughtfully as I told her what I would like. “This is too much food,” she kept saying. She had a problem with the five egg omelette. “I do not think we have a big enough pan,” she said.