“Eat, drink and be merry, for tomorrow we diet”

“Eat, drink and be merry, for tomorrow we die” is an old saying. “Eat, drink and be merry, for tomorrow we diet” is an American variant, cited in print from at least 1904.
 
“Eat, drink and be Mary” (often referring to transvestites) is another jocular variation of the saying.
 
 
Google Books
Oxford Dictionary of Proverbs
Edited by Jennifer Speake
New York, NY: Oxford University Press
2015
Pg. 88:
EAT, drink and be merry, for tomorrow we die.
A conflation of two biblical sayings: Bible (AV) Ecclesiastes 8:15 Then I commend mirth, because a man hath no better thing under the sun, than to eat, and to drink, and to be merry…and Bible (AV) Isaiah 22:13 Let us eat and drink; for to morrow we shall die. There are a number of jocular variants.
   
7 June 1904, Philadelphia (PA) Inquirer, pg. 8:
In These latter Days
Eat, drink and be merry, for to-morrow we diet.—Shanghai Times.
 
25 May 1910, Chicago (IL) Daily Tribune, “Plump Ladies Do Have a Time of It Splashing Around in a Turkish Bath” by Mme Qui Vive, pg. sec. 9, pg. 3, col. 5:
“Eat, diet, and be merry, for tomorrow we diet,” is the accepted maxim for the whole pack.
 
3 January 1918, Kansas City (MO) Star, pg. 15:
“Today,” he went on, “let us eat, drink and be merry. For tomorrow we diet.”
 
14 July 1919, Bellingham (WA) Herald, “Sayings of Celebrities” (from Cartoon Magazine), pg. 7:
Charles II—Eat, drink and be merry, for tomorrow we diet.
 
OCLC WorldCat record
Tomorrow we diet
Author: Nina Wilcox Putnam
Publisher: New York : George H. Doran Company, [©1922]
Edition/Format:   Print book : English
 
13 April 1922, Trenton (NJ) Evening Times, pg. 1:
Motto of stout people who threaten to start reducing seems to be: “Eat, drink and be merry, for tomorrow we diet.”
   
3 January 1925, Dallas (TX) Morning News, part 2, pg. 14:
The wail of the foredoomed: “Eat, drink and be merry, for tomorrow we diet.”
 
OCLC WorldCat record
For tomorrow we diet? : eat drink and be merry : the British at table 1600-2000
Author: James A Galloway
Edition/Format: Article Article : English
Publication: Lancet (London, England) Vol. 355, no. 9218 (May 27, 2000), p. 1917-1918.
Database: Wellcome Library for the History and Understanding of Medicine; History of Science, Technology, and Medicine Database
 
OCLC WorldCat record
Eat, drink, and be merry, for tomorrow we diet: Effects of anticipated deprivation on food intake in restrained and unrestrained eaters.
Author: Dax Urbszat; C Peter Herman; Janet Polivy
Edition/Format: Article Article : English
Publication: Journal of Abnormal Psychology, v111 n2 (2002): 396-401
Database: CrossRef