Every week there's a new best-selling diet book that says it's absolutely, positively the best way to drop unwanted pounds. It typically makes one or more of the following promises as well: You'll lose weight quickly, you'll lose weight effortlessly, your weight loss will be the result of some newly discovered scientific theory, and you'll look like a movie star by the time you're through.

Do these miracle diets work? Unless they're based on sound, well-researched nutritional advice, probably not (in fact, if they did work, it would be a miracle). And with so many of these newfangled fad diets out there -- how do you know which ones are dreams and which ones are duds? Read on to get the skinny.

1. A diet is not like having a second job.
Avoid any eating plan that has strict, complicated rules. Often you'll have initial success simply because of the restrictions it places on you. But such a system is so unrealistic and artificial that you can't remain on it for more than a few weeks. Take a pass on any weight loss plan where success depends on restricting certain foods, eating foods in specific combinations or timing your meals at precise intervals. A diet should be easy to follow and easily adaptable to your lifestyle.

2. If it's too low in calories, take a pass.
Know why you lose weight so quickly on those Hollywood grapefruit diets? Because they severely limit the calories you take in, often to just a few hundred calories a day. Too few calories means missing out on important nutrients, which can hurt both your short- and long-term health. Don't follow any plan that asks you to dip below 1,500 calories a day unless you're under a physician's supervision.