Dieters are often told to “watch what you eat.” Leonard Lyons’ syndicated newspaper column “The Lyons Den” reported in May 1973 that the comic actress Hermione Gingold (1897-1987) was dining at De Medici with two companions who ate full course dinners. Gingold was quoted as saying:
 
“A diet is when you watch what you eat and wish you could eat what you watch.”
 
The Gingold quotation has appeared in many collections of quotations about food and dieting.
   
 
Wikipedia: Hermione Gingold
Hermione Gingold (pronounced with a hard G, not as Jinggold; 9 December 1897 – 24 May 1987) was an English actress known for her sharp-tongued, eccentric persona, an image enhanced by her sharp nose and chin, as well as her deepening voice, a result of vocal nodes which her mother reportedly encouraged her not to remove. She starred on stage, on radio, in films, on television, and in recordings. She also appeared on the NBC interview program Here’s Hollywood.
 
Google News Archive
17 May 1973, Bangor (ME) Daily News, “The Lyons Den” by Leonard Lyons, pg. 23, col. 2:
Hermione Gingold dined at De Medici with two companions who enjoyed full course dinners. The actress lamented: “A diet is when you watch what you eat and wish you could eat what you watch.”
(The same column also appeared in the New Orleans Times-Picayune on May 14, 1973—ed.)
 
14 November 1987, Dallas (TX) Morning News:
THAT’S THE TRUTH: “A diet is when you watch what you eat and wish you could eat what you watch.”—Hermione Gingold, actress-comedian (1897-1987)
   
Google Books
Food and Drink:
A book of quotations
By Susan L. Rattiner
Mineola, NY: Dover
2002
Pg. 22:
A diet is when you watch what you eat and wish you could eat what you watch.
HERMIONE GINGOLD
 
Google Books
The Mammoth Book of Zingers, Quips and One-Liners:
Over 8,000 gems of wit and wisdom, one-liners and wisecracks
By Geoff Tibballs
New York, NY: Carroll & Graff
2004
Pg. 158:
A diet is when you watch what you eat and wish you could eat what you watch.
HERMIONE GINGOLD