His director Paritosh Painter forbid him from any kind of work out for as long as they were shooting for the film. Reason? Because Shreyas plays a girl in the movie and muscles on a girl would look as weird as, say, lipstick on a guy.
Not only that but Paritosh also asked Shreyas to give up any kind of dieting that will reflect on his body on screen. And Shreyas being a director's obedient actor didn't protest obviously because he knew it would benefit the film. Anyway, Paritosh also happens to be Shreyas' very good friend, what with them having been college pals. So, if you find Shreyas very convincing as a girl, the credit would go to Painter equally.