Complex sentence: Pratt was initially told that he was too fat to play Hatteberg, having gained 40 lbs. since he began dating Faris, which Pratt attributes to Faris' cooking.
Split into simpler sentences: Pratt was initially told that he was too fat to play Hatteberg. He had gained 40 lbs, which Pratt attributes to his then girlfriend, Faris' cooking.