The Subway diet got a lot of press, much of it from Subway itself, of course -- eat a low-fat 6-inch sub for lunch, and a foot-long one for dinner, and lose weight. It may have inspired the more negative McDonalds diet, in which a documentary director decided to eat only at McDonald's for a month. His rules included that if the counter staff suggested that he super-size something he would, and he would eat everything he ordered.

Spurlock had the idea for the film on Thanksgiving Day 2002, slumped on his mother's couch after eating far too much. He saw a news item about two teenage girls in New York suing McDonald's for making them obese. The company responded by saying their food was nutritious and good for people. Is that so, he wondered? To find out, he committed himself to his 30 days of Big Mac bingeing.

"If there's one thing we could accomplish with the film, it is that we make people think about what they put in their mouth," he said. "So the next time you do go into a fast-food restaurant and they say, 'Would you like to upsize that?' you think about it and say, 'Maybe I won't. Maybe I'll stick with the medium this time.'

Does he really think every time fast food chains offer to supersize or upsize, that customers agree to it? And if so, that they eat every bite? If they did, it would be no surprise if they gained 25 pounds, as Spurlock did, and had a skyrocketing cholesterol level. Note that he also limited his exercise during this period, although I would think simply eating far beyond the point where you feel full, several meals a day, would be the root cause for the bad effects he experienced. In other words, it's not the food itself but the quantity -- he ate an average of $28 worth of food each day, which (according to the price info I could find) means at least seven Big-mac value meals a day!

A different McDonald's month diet with different rules could easily have a very different result. I tend to agree with this woman who believes she can eat only at McDonald's for a month and lose weight. Her rules are pretty flexible but they definitely don't require her to super-size or eat every bite. Or to look at it another way, I suspect if I ate $28 worth of even Fresh Choice meals every day (particularly the pasta, muffins, etc) for 30 days I'd also gain weight.