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

New research from Johns Hopkins sheds some light.

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

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.

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