Superboy

'Superboy' is an American comic book series by DC Comics. The first volume was published between 1949 to 1977, across the Silver and Bronze Ages of comics, including two-hundred-and-thirty issues and one annual. The initial volume starred Superboy aka Clark Kent, a teenage Superman, following his adventure in the rural town of Smallville, including encounters with a young Lex Luthor and the introduction of the Superboy/Superman clone Bizarro.

Superboy Volume 1 #24: The Super-Fat Boy of Steel!
The teenagers of Smallville mysteriously become fat, with Clark and his alter ego being affected later than the others, providing Lana Lang evidence that he and Superboy are one and the same. After the mystery is solved and he slims himself down, Superboy inflates a balloon-like rubber shell under his costume to convince Lana he's still fat, and not the now-thin Clark she saw seconds ago.