The eternally boyish double Oscar winner, who drastically dieted down for Philadelphia, Castaway and Forrest Gump, only to beef up for other movies, says he can no longer let his weight fluctuate to fit the part.
"I've talked to a number of actors who have gained weight for roles and – just out of the sheer physical toll on one's knees and shoulders – no one wants to do it again," Hanks told the BBC while in London to promote his based-on-fact piracy drama Captain Phillips.
"I think that's more or less a young man's game," he said. "I'm 57 and I don't think I'm going to take on any job – or go on any vacation again – and see to it that I can gain 30 lbs."
Earlier this week, on Late Night with David Letterman, Hanks went public with his medical condition. Type 2 diabetes, which affects the body's ability to produce insulin, is generally linked to a person's weight.
"Gaining and losing of weight may have had something to do with this, because you eat so much bad food and you don't get any exercise when you're heavy," Hanks, noting that he felt "just fine," said at a London press conference for his movie.
"But I think I was genetically inclined to get it," he added, "and I think it actually and goes back to a lifestyle I've been leading ever since I was 7 years old, as opposed to 36."
Speaking to the BBC, he also revealed his (now, not so secret) food vice.
Said Hanks, "Pizza is the most delightful thing ever invented, and it's – for me – diabolically dangerous."