Shia LaBeouf is a real-life Transformer!

The 5’9″ star of the summer’s biggest action movie used to be appropriately plump. But now that he’s on the road to superstardom, he barely eats, a source tells Star. “Shia’s been living on Parliament cigarettes and black coffee, which make him lose his appetite. He probably only gets about 700 calories a day.”

The 23-year-old actor weighs in at 140 lbs. — down from a healthier 165 — according to Kansas-based certified personal trainer Marty Tuley, who has not worked with the actor.

“It looks like he went on a crash diet to lose so much weight,” says Tuley, author of the book Busting Your Butt and Gut: Minimizing Your Maximum Areas. “He’s lost all of his muscle mass to get this unhealthy thin look.”

But Shia likes his skinny frame, explains the source. “He wants to be slender. He says it makes him look better on the big screen!”

Source, Bauer-Griffin