Dev Patel struggled to gain weight for Lion

British actor Dev Patel found it "very difficult" to bulk up for his role in new drama Lion because he's always been "a little wafer".

The Slumdog Millionaire star is known for his slender physique, but after landing the lead as the adult version of real-life Indian orphan Saroo Brierley, he had his work cut out to completely transform his look.

Dev began his preparations long before shooting began, hitting the gym hard and overhauling his diet to help him build muscle, and the 26-year-old admits it was a tough few months.

"(It was) eight months of pushing weights and eating like a glutton," he told news show Access Hollywood Live, "but I had to do it because the real guy is very sporty and I'm a little wafer, so it was very difficult."

Dev then had to switch up his workout regimen after Lion wrapped to shed his muscly look and slim down for his next movie project, which is also based on a true story.

"It's called Hotel Mumbai, about the terrorist attacks that happened in 2008 in India," he explained. "I just play an average every man, so (I had to slim down)."

The actor's hard work on Lion has already paid off as the film has won critical acclaim and is hotly tipped to land Dev an acting nomination for the 2017 Oscars.

The star is flattered by the speculation, but just the thought of competing for a Best Actor Academy Award fills him with nerves.

"I don't know. It's a scary thought, that," he remarked when asked how he felt about the high praise. "It's been such an amazing tour, I've been meeting so many other great performers and actors, I do feel humbled that people are speaking about it in that way."

Lion tells the story of Saroo, an Indian boy who was separated from his family at the age of five and adopted from an orphanage by a couple in Australia. Years later, he successfully set out to find his blood relatives using the Google Earth satellite imaging app.

The movie, based on Saroo's memoir, A Long Way Home, also stars Nicole Kidman, Rooney Mara, and eight-year-old Sunny Pawar, who made his movie debut portraying Saroo as a kid.