The Rise of Duton Lang (1955)

Professor Duton Lang is an obese scientist who has made many great discoveries. When he finally weights 497 pounds he develops a compound which permits him to eat as much as he wants and still lose weight. He gets down to 150 pounds in weight but is still the same body-size as when he weighed nearly 500 pounds. Eventually, he becomes a minus-weight and floats off into outer space.