Americans have more access to information about nutrition and healthy lifestyles than at any time in history. Yet they're fatter than ever, and the obesity epidemic shows no sign of abating. So, if information is not doing the job, what would?

A new study published yesterday in the Journal of the American Medical Association offers one answer: Dieters lost more weight in less time when they had short-term incentives -- monetary rewards, in this case -- to motivate them.

The study in behavioral economics was conducted by George Loewenstein, Carnegie Mellon University professor of economics and psychology, and Kevin G. Volpp, associate professor of medicine and health care management at the University of Pennsylvania.

The researchers designed three groups and randomly assigned 57 adult participants among them. People in one group entered a daily lottery and won money if they hit their target weight. Those in the second group invested their own money but lost it if they fell short of their weight goal. A control group was monitored with monthly weigh-ins.

The weight-loss goal was the same for everyone -- 16 pounds over 16 weeks. The outcome: the incentive groups lost significantly more weight.

The lottery group earned an average of $272 and lost a mean of 13.1 pounds, with just over half meeting the 16-pound target.

The deposit group earned an average of $378 and lost a mean of 14 pounds, with just under half hitting the goal.

But the control group, which earned nothing, lost a mean of only 3.9 pounds, and only 10.5 percent met the goal.

The follow-up report will sound familiar to anyone else who has experienced the yo-yo effect of dieting. People in both incentive groups had regained some weight seven months after the rewards ended. However, they still weighed less than when they began.

The study's authors note that long-term approaches to weight loss often overlook immediate gratification.

"People can be extremely motivated to lose weight and yet fail to lose it," said Dr. Loewenstein, who studies applications of psychology to economics, law, and, in this case, medicine.

"Our take-away message is that if you have a program with very short-term incentives and feedback you can have success where long-term incentives fail."

It needn't involve money, he stressed. Weighing in daily, as the incentive groups did, instead of weekly or monthly has a short-term payoff as well.

"The message for individuals is to think on a daily basis. Get on the scale every day. If you lose weekly you'll be free and easy for the first three or four days and then try to make it up on the last days, which doesn't work," he said.

Another incentive involves changing the path of least resistance. Dr. Loewenstein and two graduate students are currently finding that if they make healthy food more convenient, they can dramatically shift people toward eating more healthfully.

"We should be making it easier to get tasty snacks that are good for you and more difficult to get unhealthy food," he said. He noted that food tastes better when you're hungry, so a healthful dinner will be more appealing if you haven't filled up on junk food.

Food labeling is still important, he said, but Americans have only gotten heavier in the 18 years since the Nutrition Labeling and Education Act went into effect.

As for the weight-loss study, he said, "It isn't so much that we're true believers in giving economic incentives. But if we're going to try to change behavior, we might as well do it in a way that's more effective and get more behavioral change bang for the buck."