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 appeared near the end of The Super Mario Bros. Super Show! episode "Mario Meets Koop-zilla"; Mario, hungry after having recently defeated Koopzilla, searched through Dr. T. Garden's laboratory and found some Shrinking Sukiyaki, which he proceeded to eat. It was only after Mario ate the Shrinking Sukiyaki that Dr. T. Garden told him of its effects, also revealing to Mario that there was no cure for Shrinking Sukiyaki and that it would take a week for its effects to wear off.