Myth: The less fat you eat, the better.

Reality: "For some people, counting fat grams can work for weight control, but it isn't the be-all end-all for people," Rosenbloom says.

She says that people with heart disease, diabetes, and metabolic syndrome may benefit from adding a little healthy fat -- the monounsaturated kind -- and cutting back on carbohydrates. But they shouldn't increase their overall fat intake -- just swap saturated fat for monounsaturated fat.

"If you go out to an Italian restaurant and you have triple cheese-meat-sausage lasagna but then you have a little olive oil on your bread, you're not doing much for your heart," Rosenbloom says.