“If it tastes good, spit it out” is old dietary advice, when so-called “health food” and “low-calorie food” frequently had little taste. The saying is of unknown authorship and appears to have been popularized from 1968-1970.
     
 
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Medical Economics
Volume 45
February 1968
Pg. 227:     
“Your diet will be simple: If it tastes good, spit it out!”
 
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Perspective: the Blue Cross magazine
Volume 4
1969
Pg. 4:
“Your diet will be simple: If it tastes good, spit it out!”
 
13 February 1970, Mansfield (OH) News Journal, “Keeping Up With All The New Worries,” pg. 4, col. 1:
As the man said, it’s almost getting to the point where “if it tastes good, spit it out.” it might be dangerous.
 
12 August 1970, Waterloo (IA) Daily Courier, “Thoughts While Weeping,” pg. 14, col. 1:
How to stay thin: If it tastes good, spit it out!
 
25 October 1970, Seattle (WA) Daily Times, pg. E2, col. 1:
Then there’s that beautiful piece of advice on dieting quoted in the Montana bulletin of the American Institute of Architects:
 
“If it tastes good, spit it out.”
 
11 November 1970, Traverse City (MI) Record-Eagle, “Pass It On” by L. M. Boyd, pg. 30, col. 1:
A CLIENT contends his doctor put him on the world’s simplest diet, prescribed as follows: “If it tastes good, spit it out.”
 
13 February 1974, Springfield (MA) Union, pg. 31, col. 7 ad:
Doctor to overweight patient: “Your diet will be simple, If it tastes good, spit it out.”
(B.F. Goodrich—ed.)
   
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Making It Big:
A guide to health, success, and beauty for the woman size 16 and over
By Jean DuCoffe and Sherry Suib Cohen
New York, NY: Simon and Schuster
1980
Pg. 14:
I’ve only found one diet that ever worked. A wise old doctor gave it to me. This is it: If it tastes good — spit it out. Would you live your life that way? Not me.
 
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Strictly for Laughs
By Joey Adams
New York, NY: A & W Publishers
1981
Pg. 130:
I got the simplest diet of all— if it tastes good, spit it out.
 
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The Better Life Institute Family Health Plan
By Steven M. Zifferblatt, Patricia M. Zifferblatt and Norm Chandler Fox
Nashville, TN: T. Nelson Publishers
1991
Pg. 60:
The old saying, “If it tastes good, spit it out,” is just that— old, out-dated, no longer true! Today’s food products make it possible to eat a heart-healthy diet that tastes delightful.
     
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Simply Southern Ease:
More Humor, Insights and Fun from a Good Old Southern Gal
By Cappy Hall Rearick
Lincoln, NE: iUniverse
2006
Pg. 134:
“The cardiologist’s diet: If it tastes good, spit it out.”—Author Unknown
   
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So? Whatever!:
365 Laughs and Devotionals
By Charles Jones and Mary Crisp
Bloomington, IN: CrossBooks
2010
Pg. 126:
The doctor told him there was a diet guaranteed to work. The man then asked, “What type of diet is that?” The doctor responded, “Put it in your mouth, if it tastes good, spit it out.”
 
The Notes:
Ronald Reagan’s Private Collection of Stories and Wisdom
By Ronald Reagan
Edited by Douglas Brinkley
New York, NY: HarperCollins
2011
Pg. 191:
Simple diet—if it tastes good spit it out.