Weight Watchers is more effective for weight loss than physician assisted programs.

In some ways this comes as a surprise, in other ways it seems logical that a group committed to nothing but weight loss and maintenance would be the hands down winner.

People in the Weight Watchers group were three times more likely than the other participants to lose 10% or more of their initial body weight. And nearly two-thirds of the Weight Watchers users lost 5% or more of their body weight, versus one-third in the other group.
“Those really are medically very significant numbers,” Jensen says. “For overweight or obese people, that kind of loss results in pretty substantial improvements in health and disease risk—to the point where, if you’re on medication for blood pressure or cholesterol or diabetes and you can [lose] 10% of your weight, you’ve got at least a reasonable chance of decreasing or discontinuing that medication.”