Urusei Yatsura S01 E26 Full Course from Hell

"Grab her horns and she might just become your darling!"

Still at the resort, the group meets some maniac who is having an all-you-can-eat contest. Sakura reveals the secret of her figure to be a diet pill called "Beauty Foods". But we really know the real reason is Sakura can just plain eat like a whale, and we see her do so as she beats Ataru and Cherry in the contest and clean the maniac of all his food.