Kristen Stewart has reportedly put boyfriend Robert Pattinson on a diet.

The 22-year-old actress - who also plays Robert's on-screen lover in the 'Twilight' franchise - has apparently ordered him to hit the gym and lose some of the weight he's gained during his time off.

A source said: ''Robert's put on nearly 10lbs eating cheeseburgers and drinking beer while he's not been working.

''Kristen's told him to pull himself together. He hates the gym, so she's encouraged him to take up paddle surfing to try and work off the excess calories.''

But the 'Water for Elephants' star did not seem to be too upset by the constructive criticism when he splashed out on film-making equipment for Kristen's 22nd birthday.

The insider told the Daily Star newspaper: ''Robert has been searching shops in Hollywood for movie equipment.

''Kristen's always dreamed of being behind the camera. He also organised a big banquet.''

However, he has previously admitted to living in fear of shirtless scenes, especially when they involve his buff 'Twilight' co-star Taylor Lautner.

He said: ''I'd have to make a lifestyle change if I wanted to do shirtless acting. But it seems like every single actor in the world is doing a 'Taylor Lautner' scene - it's crazy.

''They have a scene where they walk out with like a 12-pack. It's like, 'Really? You're playing a normal guy! That doesn't make any sense.' But that's a prerequisite of being an actor. Or you can get fat!''