PHILADELPHIA (CBS) – Ever wondered which diets truly work?

New research from Johns Hopkins sheds some light.

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Researchers say they looked at 11 programs to compare weight loss, adherence and possible harm.

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Only Weight Watchers and Jenny Craig helped people lose the pounds and keep it off for at least a year.

Other programs, like Nutrisystem, had great immediate results, but scientists say more research is needed to determine the long term effects.

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The research was published Monday in the Annals of Internal Medicine.