Many actors have to gain/loose considerably for their respective characters in the movie as as per the requirement of the script. And they have to do it, within limited time frame. Similar thing happened to Salman Khan for his last movie Sultan. he had to gain several kilos,. and he said it was indeed a painful experience for him to go from fit to fat.
At the recently held Zee Cine Awards, on being asked about teh same, Salman replied “There is a lot of pain in undergoing physical transformation. I have been training for Tiger Zinda Hai and there is another film that I am training – it’s a dance film (referring to Remo D’Souza film). For Sultan, I was 96 kgs. I have shed 18-20 kgs.”