Prunes are known to be nature’s laxatives. The bumper sticker “Start A Movement—Eat A Prune” (a joke on “bowel movement") has been cited in print since at least 1973.
Prunes and their juice contain mild laxatives including phenolic compounds (mainly as neochlorogenic acids and chlorogenic acids) and sorbitol. Prunes also contain dietary fiber (about 6%, or 0.06 g per gram of prune). Prunes and prune juice are thus common home remedies for constipation. Prunes also have a high antioxidant content.
4 February 1973, The Sun (Baltimore, MD), “State’s legislators face a social 2 weeks,” pg. A14:
“It read: ‘Start A Movement, Eat A Prune.’”
18 August 1973, Nevada State Journal (Reno, NV), pg. 5, col. 1:
Two bumper stickers sighted this week impart profound messages:
Support Mental Health—or I;ll Kill You;
And: Start a Movement—Eat a Prune.
19 May 1974, The Independent Record (Helena, MT), “A bumper crop of stickers,” pg. 17:
START A MOVEMENT
EAT A PRUNE
Reporting for the Print Media
By Fred Fedler
Fort Worth, TX: Harcourt Brace Jovanovich
Another student appeared for an interview dressed in a T-shirt inscribed, “Start a Movement—-Eat a Prune.”
Only Begotten Daughter
By James Morrow
San Diego, CA: Harcourt Brace
At least she was dressed for the heat: denim cutoffs, a Smile Shop T-shirt (start a movement — eat a prune).
The Mammoth Book of Humor
Edited by Geoff Tibballs
New York, NY: Carroll & Graf
Eat a prune and start a movement.