The Fat Guy Strangler is episode 17 of family guy season 04. It was originally aired on November 27, 2005.
When Lois drags Peter to the doctor for a physical, his diagnosis is clear: he’s too fat. This news drives Peter to form the NAAFP, an advocacy group for the advancement of fat people. Meanwhile, Lois discovers her long-lost brother, Patrick, and fights to get him released from an insane asylum. But a string of fat guys go missing soon after, and Peter and the NAAFP band together to get to the bottom of it.