In a review of 10 separte studies of weight-loss programs, scientists found few hard evidence to support their claims that they help people lose weight.
Only Weight Watchers had scientific research to back up its simple approach of keeping a food diary and focusing on low-calorie foods, especially vegetables and whole grains, according to a study being published Monday in "The Annals of Internal Medicine."
"With the exception of one trial of Weight Watchers, the evidence to support the use of the major commercial and self-help weight-loss programs is suboptimal," Dr. Adam Tsal and Thomas Wadden of the University of Pennsylvania wrote.
The largest trial showed dieters using the Weight Watchers program lost and kept off 3.2 percent of their weight after two years.
Weight Watchers guides people toward healthier lifestyle choices over the long term, said Nutrition expert Dr. David Katz.
Katz suggested that people should consider three factors — permanence, family and readiness, while choosing any weight loss program.
Permanence means will I learn something or acquire a skill I can use forever? If it's about a short-term program, you get on, you get off, you lose weight, and in a while it'll come back on," said Katz.
The program also has to take family members into consideration, he said, because it's difficult to stick with a program that doesn't include the rest of your household.
But perhaps most important, the dieter has to be ready to make the commitment to a program.