British actor Jeremy Irvine adopted an extreme tuna-based diet to lose weight for his role in The Railway Man.

The War Horse star portrays World War Ii soldier Eric Lomax, who is sent to work on the Japanese army's infamous Thai-Burma railway in 1942, with Colin Firth playing the character's older incarnation.

The Brit had to drop nearly 28 pounds (12.7 kilograms) in order to accurately resemble a starving and malnourished prisoner of war, and he managed the dramatic weight loss by living off a single can of tuna each day.

Irvine tells Britain's InStyle magazine, "It's called the no-more-than-one-can-of-tuna-a-day diet. I lost almost 28 pounds. You're so hungry the whole time you lose your mind a bit. I had no energy and kept having really mad dreams, which alarmed my parents slightly. We had a dietitian on set to keep an eye on me.

"For someone of my generation, it's impossible to relate to what prisoners of war went through. I owed it to Eric to make it look as realistic as possible."