How to lose weight

What saved Hamaski just in time was Fatbet.net. In February he and five friends bet on losing 9.9kg in eight weeks. "I became very competitive, it was a matter of honor," the Californian says. Every day Hamaski and his friends had to register their weight on the website. They also invited their families and other friends to follow the collective slimming online.

"There was a lot of pressure, I didn't want to be a loser." Thanks to the bet, Hamaski forced himself to eat a balanced diet and to exercise six times a week. In the end, he actually won the bet. "In April I was down to 74kg."

Hamaski's story is not an isolated case in the United States. Thousands of Americans use websites like Fatbet.net as another option to traditional diet programs, such as Weight Watchers, Atkins and Slim Fast.

"These bets are working wonders. People don't want to lose and they really succeed in reducing their weight," believes Fatbet founder Adam Orkand, 40. Since launching the website in January 2008, about 6,000 users have signed up on Fatbet.net. Most of them are successful: 80 percent win their bets by losing a few pounds.

But if someone tries to lose 50 pounds (23kg) at once it certainly won't work. On average every Fatbet user loses 14 pounds (6kg) - without paying any fees because the website is financed through ads.

"The most important thing is the wager," explains Orkand. "It has to be something that you definitely don't want to lose." There are no limits, wagers can be anything: Losers have to let their beards grow, sing embarrassing songs in karaoke bars or run naked through a city center. But often it is all about honor - or cash.