No. 9 (tie) The Engine 2 Diet

Experts were impressed with the Engine 2 Diet, a low-fat, vegan plan designed to prevent and perhaps reverse diseases like diabetes caused by the so-called standard American diet. It will almost certainly help you lose weight, which can stave off Type 2 diabetes. Plus, one study found that those on a similar diet were able to ease up on their diabetes medications and lower their A1C hemoglobin levels.

But, as with any restrictive plan, careful planning to consume the right amount of various nutrients is key. "Following this diet alone will not reverse diabetes; you'd still have to pay attention to carbohydrate intake," one reviewer said.