Mila Kunis, 'Black Swan' and how extreme diets warp your body Mila Kunis attends the Christian Dior Ready-To-Wear Fall/Winter 2012 show as part of Paris Fashion Week at Musee Rodin on March 2 in Paris, France. Losing weight like a star may seem like a dream come true. With a personal trainer, personal chef, personal dietitian and personal assistant at your side, who couldn't shed 20 pounds in a few short weeks? But a new interview with actress Mila Kunis in Harper's Bazaar indicates that fast weight loss (in this case for a role) can sometimes result in fast weight gain -- in all the wrong places. Already lean, Kunis dropped 20 pounds in order to play Natalie Portman's ballerina frenemy in "Black Swan." At 95 pounds, Kunis says "I was muscles, like a little brick house, but skin and bones." Unfortunately, when she gained the weight back, Kunis says it ended up in completely different places. "All the weight that left my chest went to my side hip, my stomach," she told the magazine. Andrea N. Giancoli, a registered dietitian and spokeswoman for the Academy of Nutrition and Dietetics, says redistributed weight isn't uncommon after drastic weight loss (and weight gain). "What often happens with extreme weight loss and when you lose weight very quickly is that you lose muscle tissue," she says. Unfortunately, when we gain the weight back, it comes back as fat. And that fat tends to show up wherever you're genetically predisposed to get it. "Some people store fat in their bellies, others in their thighs or their breasts or their buttocks," she says. Wherever you typically store fat, you're going to see it go back there. What's more, fast weight loss usually affects your metabolism, slowing it down so your body will burn the calories it gets more efficiently. "You turn down the fire of your body furnace," she says. But when you go back to eating normally again, that furnace is still turned down to low, therefore you gain weight more easily and you gain it as fat, unless you're really diligent about not overeating and exercising. If you're dieting, Giancoli advises you shoot for losing 1-2 pounds a week, which gives your body opportunity to adapt to the weight loss and minimizes the loss of lean tissue and muscle. As for celebrities and their weight-related ups and downs, she says they're often a perfect example of what not to do. "Celebrities are great Petri dishes for us in a way," she says. They demonstrate what happens with extreme weight loss. We'll hear that so-and-so lost 20 pounds in 20 days and we'll see her all thin and gorgeous. Then a few months down the line, she'll have gained all the weight back because she did it too rapidly. And we blame the celebs, not the ridiculous diets. But really, it all comes down to human physiology and biology. Your body doesn't like it when you lose weight that fast. Have you noticed that your body behaves in weird ways after a crash diet? Tell us about your experiences on Facebook.