"Eat, drink and be merry, for tomorrow we die” is a saying from the Bible (Isaiah 22:13).

“Eat, drink and be merry, for tomorrow we diet” is an American variant, cited in print from at least 1904.


Bible Commenter
Isaiah 22:13
Geneva Study Bible
And behold joy and gladness, slaying oxen, and killing sheep, eating flesh, and drinking wine: let us {p} eat and drink; for to morrow we shall die.

(p) Instead of repentance you were joyful and made great cheer, contemning the admonitions of the prophets saying Let us eat and drink for our prophets say that we will die tomorrow.

Answers.com
Eat, drink, and be merry for tomorrow we die
A conflation of two biblical sayings: ecclesiastes viii. 15 (AV) Then I commended mirth, because a man hath no better thing under the sun, than to eat, and to drink, and to be merry ‥ and isaiah xxii. 13 (AV) Let us eat and drink; for to morrow we shall die. There are a number of jocular variants (see for example quot. 2001).

Eat thou and drink; tomorrow thou shalt die.
[1870 D. G. Rossetti ‘The Choice’ in House of Life, Sonnet lxxi.]

But far from prompting him to repeat the maxim ‘Let us eat and drink, for tomorrow we die!’ it spurred him rather to a sort of fiery energy, never satisfied with what it had accomplished.
[1884 E. Lyall We Two xii. 240]

Inchcape‥complained: ‘I’ve never before seen this place in such a hubbub.’ ‘It’s the war,’ said Clarence. ‘Eat, drink and be merry, for tomorrow we may be starving to death.’
[1960 O. Manning Great Fortune (1988) 42]

No point in getting morbid. ‥What the hell. Eat, drink, and be merry, and all that crap. Lukas signaled the waiter and ordered another two croissants.
[1975 N. Guild Lost and Found Man 87]

Eat, drink and be merry, for tomorrow we diet.
[2001 New Scientist 22/29 Dec. 45]

7 June 1904, Philadelphia (PA) Inquirer, pg. 8:
In These latter Days
Eat, drink and be merry, for to-morrow we diet.—Shanghai Times.

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.

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) , part 2, pg. 14:
The wail of the foredoomed: “Eat, drink and be merry, for tomorrow we diet.”