The actor said that he was tired of having his ab muscles compared to co-star Taylor Lautner's, and confessed that he gave up on his diet and exercise regimen immediately after shooting finished.
"This is so unfair doing a comparison. Everyone says I painted on my abs in [New Moon] - I did not! Taylor has his painted on too!" Pattinson told MTV News.
"I had it for, like, two weeks. As soon as I didn't have to be shirtless anymore [my good habits were] gone immediately. During [filming in] Brazil, the day before I had to do my shirtless scene, I realised [my abs] weren't as good as Taylor's, so I just ate every bit of chocolate in the mini-bar. I started eating cheeseburgers and stuff."
Pattinson previously confessed that he was "worried" about appearing shirtless on-screen and felt uncomfortable disrobing on camera.
Breaking Dawn co-star Kristen Stewart also expressed apprehension over the intimate scene, saying that the public's expectation is high for Bella and Edward's first sexual encounter.
Watch a trailer for The Twilight Saga: Breaking Dawn - Part 1 below: