The actor had to put on 50 lbs (23 kg) during pre-production to make him look like a middle-aged man. When Tom Hanks was in this shape, they shot the parts of the film before the island scenes, and then took a year off to let Tom lose weight to impersonate a real cast away. He didn’t shave or cut his hair for weeks and shed 55lb in four months with a diet and a tough exercise regime.
“The idea of looking at four months of constant vigilance as far as what I ate, as well as two hours a day in the gym doing nothing but a monotonous kind of work-out was formidable. You have to power yourself through it almost by some sort of meditation trickery. It’s not glamorous,” Hanks said.
His diet consisted mainly of: crab, fish, vegetables, very little carbohydrate from fruits, coconut milk and water. When Hanks felt hungry, he ate large amounts of vegetables. This allowed him to consume natural food without having to go hungry between meals. This diet later became famously known as the Castaway Diet.