There are lots of do's and don'ts when it comes to dieting, and relying on fad diets is one of the biggest no-nos out there. But just what constitutes a fad diet? Here are a couple of rules of thumb:

• Any diet that makes you cut out one or more food group -- or solid food altogether -- is probably a fad diet (like that Lemonade diet -- ugh).
• Speaking of that, any diet that limits your meals to the same rancid thing over and over again is a fad diet.
• Any diet that that makes you fork out money for pills or special formulas for is a fad diet.
• Any diet that limits you to less than 1,000 calories a day is a fad diet -- and a really dangerous one at that!
• And sorry folks, any diet that promises you'll lose more than a couple of pounds a week is a fad diet.

If you've fallen for these in the past, don't beat yourself up -- celebs like Liz Hurley and Sarah Michelle Gellar have tried the Cabbage Soup Diet just like you. Bottom line? They just don't work. Well, they might, but not in the long run.

Instead, take some healthy advice from Drew Barrymore -- she recently told reporters, "My top beauty and fitness tip is to eat whatever you want in smaller increments but don't starve yourself to societal pressures. And I love to exercise because it makes me feel good about myself." Amen, sister.