From the Super Mario Wiki
Shrinking Sukiyaki is an invention of world-renowned scientist Dr. T. Garden. Once eaten, Shrinking Sukiyaki causes the ingester to shrink to minuscule size for at least a week.
Shrinking Sukiyaki appears near the end of The Super Mario Bros. Super Show! episode "Mario Meets Koop-zilla"; Mario, hungry after having recently defeating Koopzilla, searches through Dr. T. Garden's laboratory and finds some Shrinking Sukiyaki, which he proceeds to eat. It is only after Mario ate the Shrinking Sukiyaki that Dr. T. Garden tells him of its effects, also revealing to Mario that there is no cure for Shrinking Sukiyaki and that it only takes a week for its effects to wear off.