What is the most telling sign that a food fad has reached critical mass? In the case of the rampant carbohydrate phobia, for instance, is it the fast-food bandwagon (the Burger King Bunless Whopper, served on a plate with knife and fork)? A new line of ice cream flavors (Ben & Jerry's Carb Karma)? Or the innovative marketing of laxatives to legions of constipated Atkins dieters ("a zero-carb solution to a low-carb problem")?

So are carbs the problem? Should we ban them from our diets? "The fear of carbohydrates is a response to one or two studies that showed that under specific conditions, a diet heavy in easily digested, simple carbs may raise the risk of heart disease, diabetes, and obesity," says Kritchevsky. There's a nugget of truth in all this, but more research is needed to tease out the fad from the fact. Here's what science knows now.