ROBERT Pattinson would be a "fat arse" if he wasn't an actor.

The 29-year-old actor is thankful for the "vanity" of Hollywood as it ensures he stays in shape, but admits that is getting increasingly more difficult as he gets older.

He said: "I'm so glad about the vanity required in this job because if I didn't have to stay in shape, I'd be such a fat arse, but it used to be that I could start working out four weeks before a job and it would be totally fine.

"Now? Nothing happens. You just beat your body into submission. What the f**k is going on?"

And the 'Life' actor - who is engaged to singer FKA twigs - admitted he even went on holiday to an "extravagant secret location" to avoid his portly physique being ridiculed.

He added: "I had to go on holiday to an extravagant secret location this year because I was afraid of someone photographing my gut."

Despite his career success, the British star admits his "entire mind falls apart" before he starts work on a new movie because he worries being exposed as a "fraud".

He told The Times newspaper: "[I have] a constant fear of being found out and humiliated as an actor.

"A month before I start a job, my entire mind falls apart, [worrying about] unfathomable depths of disaster.

"It's so difficult not to just think that you're a fraud."