Stars who gained lost weight for roles

Ever since Robert De Niro gained 60 pounds to play washed-up boxing champ Jake LaMotta in the 1980 film "Raging Bull," actors have been using extreme weight loss and gain to help transform themselves into their on-screen characters.

Colin Farrell appears to be the latest. A recent photo snapped in Spain shows an emaciated Farrell with hollowed cheeks, sunken chest and stick-thin legs. It is believed that he shed the weight for his latest role as a Bosnia War photographer in a new film called "Triage," which is currently shooting in Alicante, Spain.
While these days it seems everyone in Hollywood is trying to pull a De Niro, shape-shifting actors can earn the kudos and respect of their peers. George Clooney in "Syriana" and Charlize Theron in "Monster" both won Academy Awards after they packed on the pounds. Renee Zellweger and Tom Hanks were both nominated after they gained and lost weight, respectively.

Some doctors worry that such dramatic transformations can give audiences the wrong impression that they can fatten up and drop weight in a flash.

"It's not as easy as it looks," Madelyn Fernstrom, associate professor and director of the Weight Management Center at the University of Pittsburgh Medical Center, told ABC News.com. "I counsel patients all the time that these people have medical monitoring, special diets and exercise regimens."

In actual fact, losing or gaining weight that fast is not good for your health. It causes kidney stones, stretch marks and not to mention it promotes yo yo dieting.