For 15 years, the British bookmaker William Hill allowed bettors to wager on their own weight loss, often taking out full-page newspaper ads to publicize the bet.  This was a clear opportunity for those looking to lose weight to make a commitment, with real teeth.  Here is a paper by Nicholas Burger and John Lynham which analyzes the data.

Descriptive statistics are presented in Table 2, which shows that 80% of bettors lose their bets. Odds for the bets range from 5:1 to 50:1 and potential payoffs average $2332.9 The average daily weight loss that a bettor must achieve to win their bet is 0.39 lbs. In terms of reducing caloric intake to lose weight, this is equivalent to reducing daily consumption by two Starbucks hot chocolates. The first insight we draw from this market is that although bettors are aware of their need for commitment mechanisms, those in our sample are not particularly skilled at selecting the right mechanisms.10 Bettors go to great lengths to construct elaborate constraints on their behaviour, which are usually unsuccessful.

Women do much worse than men.  Bets in which the winnings were committed to charity outperformed the average.  Bets with a longer duration (Lose 2x pounds in 2T days rather than x pounds in T days) have longer odds, suggesting that the market understands time inconsistency.

Beanie barrage:  barker.