Michele Rouse holds a salad that she made in her kitchen in Edgewood, Md on Apr. 3. Rouse says she has lost 7 pounds since she started Weight Watchers a month ago and has already seen a drop in her elevated blood pressure. Weight Watchers and Jenny Craig scored the best marks for effectiveness in a review of research on commercial diet programs, but many other plans haven't been studied enough to evaluate long-term results. (AP/Patrick Semansky)

Looking to shed those extra pounds? If you've ever wondered which commercial weight loss plans in the crowded market are worth the money, scientists now have an answer. Or at least a partial answer.

In a new journal article published on Tuesday, scientists found that there's only enough evidence to conclude that two of the 32 major plans -- Weight Watchers and Jenny Craig -- will keep weight off for at least a year. Researchers Kimberly Gudzune and Ruchi Dosi from Johns Hopkins University noted that some other popular programs, and Nutrisystem specifically, show "promising" results, but that more work is needed to evaluate whether the effects will last for the long-term.

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The study found that at 12 months, Weight Watchers participants saw at least a 2.6 percent greater weight loss than those not on the plan, while Jenny Craig resulted in a 4.9 percent greater weight loss. That compares with 0.1 percent to 2.9 percent for Atkins during a similar time period, according to the study which was published in the Annals of Internal Medicine on Tuesday. Participants saw a greater weight loss at six months for very low calorie plans -- at least 4 percent for Medifast and OPTIFAST -- but that initial loss appeared to taper off in subsequent months.

Weight loss is a $2.5 billion and growing industry in the United States. With more than a third of U.S. adults obese and many more seeking to lose that extra 10 to 15 pounds, commercial weight loss programs -- which cost anywhere from around $50 to $700 a month -- have become increasingly popular tools. But physicians haven't had a lot of information to be able to recommend certain commercial programs, other diets or education and counseling.

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A previously published study in the Journal of the American Medical Association in September 2014 found that low-carb and low-fat diets in branded weight loss programs -- those that are recommended through books, or in-person or online -- seem to work similarly well. "Despite potential biological mechanisms explaining why some popular diets should be better than others, recent reviews suggest that most diets are equally effective, a message very different from what the public hears in advertisements or expert pronouncements," the researchers wrote.