A group of researchers conducted a study primarily focused on several weight loss programs and discovered that only two of them were actually effective in accomplishing the desired goal.

The study, which was conducted by the researchers at John Hopkins University, looked at 4,200 already published studies that focused on weight loss programs. The researchers found just a few dozen of the previous studies were rigorous or efficient enough to be included in their analysis. For the study, the researchers looked at 11 major weight loss programs.

Kimberly Gudzune, M.D., M.P.H., an assistant professor of medicine and a weight-loss expert at the Johns Hopkins University School of Medicine, said, “Primary care doctors need to know what programs have rigorous trials showing that they work, but they haven’t had much evidence to rely on.”

The researchers found that only Jenny Craig and Weight Watchers were found to produce distinguishing weight loss results in the studies that were analyzed. The customers of Jenny Craig were discovered to lose nearly five percent more weight than their counterparts who were not dieting. On the other hand, Weight Watchers clients were found to lose about three percent more weight.

“Our review should give clinicians a better idea of what programs they might consider for their patients,” Gudzune said in a statement.

The findings of the study were detailed in the journal Annals of Internal Medicine.