The Fairly OddParents S05E05 - Just Desserts

Timmy, unhappy that he has to eat healthy foods all the time, wishes that everyone ate nothing but dessert. This leads to rushes in energy at first, but its side effect soon kicks in: everyone becomes unusually overweight, which Timmy sees as a partly good thing (no one is made fun of for being fat/Francis tries to pick on fit kids (Mark), making him too fat to even move), but this leads to causing the Earth to fall and almost crash into the sun. Timmy saves the day by feeding spinach--recovered from Mark's ship--to his fairies so they can undo the wish.