Billy Bob Thornton on special regime

Billy Bob Thornton has revealed details about a rare health condition that requires him to strictly control his diet.

"I'm allergic to wheat and dairy. I have AB negative blood type, which is the rarest in the world. Less than 1 percent of the world's population has it," said Thorton.

The "Bad Santa" actor said that his rare blood type, at least in his case, also causes digestive problems, in addition to other dietary restrictions.

"It means you have fewer digestive enzymes. That's one of the things that goes along with it," he explained.

Thorton, who spent his childhood in Arkansas and Texas, said he grew up with many allergies but "ate everything."

"I just thought everyone felt bad after eating. I didn't know. But anyway, I'm not allowed to eat dairy, wheat... I'm not allowed to eat meat, like pork or beef," he said.

Torton first learned about the rare blood type in the late 1980s, after which he eliminated wheat, dairy products, red meat and other foods from his diet.

"I call myself a vegan who cheats sometimes, but I don't cheat a lot."