I remember seeing Fatso for the first time in Madison, WI in 1980 and I thought it was a sad but funny movie. It was sad throughout several portions of the movie, including the opening scene when the DiNapoli family gathered at the funeral of cousin Sal, who died of obesity, motivating Dom's sister Antoinette (hysterically portrayed by Anne Bancroft in her movie debut as writer and director) to persuade him to make an appointment with the diet doctor.
Things go well until he threatens his brother (Ron Carey) with a knife and goes nuts and starts crying in self-pity and binges with his Chubby Checkers Sonny and Oscar. Meanwhile, things get back on track when he falls in love with Lydia, played by the lovely Candy Azzara but one day she's not home and Dom is so distraught so he eats a humongous order of Chinese food. Once again he wallows away in tears of self-pity. Once he finds out that Lydia is OK, things get back to normal, they get married and they live happily ever after.
There was one other scene that cracked me up. The scene where Dom bought a birthday cake for his nephew Anthony and he ate part of it, causing Antoinette to get hysterical and throw the cake around.
It's a shame that Dom DeLuise, who played Dom so well in his first starring role in a movie, Bancroft and Carey are gone. Fatso should be seen as a tribute to a fine and funny cast. Don't see it on an empty stomach.