Mumbai:Actor Vivek Oberoi, who will need to lose about 18 kg to shoot some parts of gangster film "Rai", says it's important for him to follow the right weight-loss process. Vivek needs to lose weight for a younger avatar for the initial sequences of the film. The 39-year-old star says that as an actor, physical transformation is sometimes required for roles. "As an actor, we need to transform ourselves physically for certain roles. For me, losing or gaining weight is not important, but the right process has to be followed so that it doesn't affect me in the long run," Vivek said in a statement. The "Saathiya" actor has been following a liquid diet for almost a month, said a source close to him. "Vivek's dietician has asked him to drink a lot of hot water, juices and herbal liquids post which he will start weight training and also a mix of cardio and yoga," the source said. The actor will be seen playing the character of former underworld don Muthappa Rai in Ram Gopal Varma's "Rai". This is not the first time that Vivek will be seen playing a character with a negative shade. He has previously essayed characters like a gangster, a criminal and even an underworld don on screen.