Mr. Ee, 30, worked at an Internet company in SoHo, and had been competing with a colleague to see who could lose more weight. But they had both stopped going to the gym because of long hours at the office. In search of more motivation, they turned up the pressure: they entered into a formal one-month wager to see who could cut the higher percentage of their body mass index.
His co-worker, Daniel Fries, won the first month, after losing about 16 pounds to Mr. Ee's 10, and Mr. Ee paid him $20.
Then, Mr. Ee said, "it got serious."
Six co-workers joined them in another weight-loss competition. "I told them this was going to be dirty," Mr. Ee said. There were weekly weigh-ins by an outside record keeper. Mr. Ee finished second in that bet, after losing an additional four pounds. Along the way, Mr. Ee's officemates enjoyed taunting one another with comments like, "Are you sure you want to eat that bagel?" and "Why don't you get a cheeseburger for lunch and I'll get a salad?"
It was an eight-player example of a diet bet, in which those seeking to lose pounds give themselves a new incentive: money. If they don't lose more weight than the competition, they lose cash. Internet sites that facilitate diet betting have seen an increase in traffic, and recent studies have supported what Mr. Ee and his co-workers discovered: diet bets work for many people who couldn't seem to shed pounds any other way.