Falling from the No. 1 spot to the No. 6 spot this year is the king of the low-carb craze. Controversial in both the U.S. and abroad, proponents argue that the Atkins diet is a healthy way to lower your "bad" cholesterol as well as lose weight quickly, while critics say it's not sustainable for lasting weight loss.
Although starting with the plan's super low-carb diet and progressing through the phases to add slightly more carbohydrates has been shown to be moderately successful for tightening your belt, the fact that you're allowed to eat fatty foods with abandon worries most health experts.