If you're invited to a Barmecidal feast, it is recommended that you eat beforehand.

Barmecidal (or Barmecide) describes something that provides only an illusion of plenty and abundance. The adjective derives from the name of a rich and powerful ruling family in 8th-century Persia, the Barmecides, or Barmakids. One of the Barmecides was the subject of a tale told in the The Arabian Nights' Entertainments. This story led to the figurative use of the Barmecide name.

The Barmecide prince, it is told, invited a local beggar, Schacabac, to dinner. The prince served the hungry man course after course of empty dishes, pretending that they amounted to a sumptuous banquet, in order to test the beggar's sense of humor. It was Schacabac who had the last laugh, however. Schacabac went along with the prince's joke, pretending to enjoy his illusory meal. Upon being offered some imaginary wine, the beggar pretended to fill and refill his goblet. In feigned drunkenness, he clumsily knocked the prince over. Amused rather than angry at Schacabac's actions, the prince rewarded the good nature of the beggar with a real feast.

The imaginary meal led to the use of the prince's name to mean an illusion of abundance. Thus, nowadays, a Barmecidal feast, banquet, meal, etc., is one that, however inviting to the eye, fails to satisfy or live up to expectations.