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Researchers have spent years studying the keys to weight loss. Here are some significant findings:
* Dieters who keep a daily food record usually lose more weight, says Thomas Wadden, director of the Weight and Eating Disorders Program at the University of Pennsylvania School of Medicine in Philadelphia.
People eat less when they keep track and are more likely to meet their daily calorie goals.
* One diet doesn't fit all. ''The biggest change in the past several years is the realization that one diet doesn't work for everyone,'' Wadden says.
It used to be that everyone advised following a low-fat, balanced diet based on the government's food guide pyramid, he says. Now studies show that the Atkins diet works for some people and appears to be safe for six months to a year. At the end of a year, the two approaches produce comparable weight losses.
* Dieters achieve two-thirds of their ultimate weight loss in the first three months on a program and the remaining third in the second three months, after which weight loss typically stops, Wadden says.
There may be several explanations for this. ''People may be the most adherent to their plan early on because it hasn't gotten too dull or depriving. And as time goes on, the weight loss also slows because of reductions in resting metabolic rate, which determines people's calorie requirements.''
Plus, there are physiological reasons why it's difficult for people to lose more than 5% to 10% of their body weight. There are several hunger hormones that change with weight loss and increase appetite as the body fights hard to return to its baseline weight, Wadden says.
Although most medical experts consider a 20-pound weight loss a success, many dieters don't see it that way, he says. ''They see what they haven't lost rather what they have achieved.''
His suggestion: Lose 10% of your total weight, then try to maintain it for a while. After several months, try to lose another 5% to 10%.
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