According to Chris, Robert was too tubby to play the title role in Sherlock Holmes.
"He's a huge Sherlock Holmes fan," Robert said of Chris.
"He said to me before we began, 'You've got to be gaunt. You've got to be a skinny as you possibly can to play Holmes.' So every time I'm reaching for a muffin I just think about Chris Martin and skip the snack. It's been tough."
Rob had been piling on the pounds for his role in Tropic Thunder. "All I did was eat cheeseburgers and smoke Camels for three months," he said. "You've got to be in good shape to make it through that.
"I do tons of weightlifting and martial arts anyway, so I stepped up my Wing Chun Kung Fu. I like staying in shape for a movie. Normally you pay for personal trainers, so it's great when you can keep fit at someone else's expense. I run a lot of miles and eat a lot of Wheaties cereal."