Food author Michael Pollan wrote in Food Rules: An Eater’s Manual (2009):
   
“Eat all the junk food you want, as long as you cook it yourself.”
 
Pollan came up with the rule by at least February 2008, explaining in a newspaper article that special-occasion food (such as cakes, pies and ice cream) was okay to have if one cooked it for one’s self—that is, it would be cooked and consumed rarely. Pollan’s food rule has been frequently cited.
 
 
Wikipedia: Michael Pollan
Michael Pollan is an American author, journalist, activist, and professor of journalism at the UC Berkeley Graduate School of Journalism.
   
27 February 2008, Anniston (AL) Star, “Food research distilled to 7 words” by Rebekah Denn (Seattle Post-Intelligencer), pg. 4D, col. 4:
In his latest book, In Defense of Food, Michael Pollan neatly distills decades of food research into seven words. (“Eat food. Not too much. Mostly plants.”)
(...)
On what he’s learned since the book’s publication:
I’ve come across a lot of really great tips. (...) I’ve thought of new ones myself: “Eat all the junk food you want, as long as you cook it yourself!” Which focuses on the idea that special-occasion food is fine, but with this corporatization of our food it’s possible to have special-occasion food three times a day. I know, because my son loves broccoli tempura more than anything. He would have it every day, but he doesn’t want to cook it every day, and that’s the condition of him having it. We cook together. ANd that puts special-occasion food back where it needs to be.
 
Google Books 
Food Rules:
An Eater’s Manual
By Michael Pollan
New York, NY: Penguin Books
2009
Pg. 85:
Eat all the junk food you want as long as you cook it yourself.
There is nothing wrong with eating sweets, fried foods, pastries, even drinking a soda every now and then, but food manufacturers have made eating these formerly expensive and hard-to-make treats so cheap and easy that we’re eating them every day.
   
Twitter
Ralph Loglisci
‏@R71
Last Pollan Food Rule for a while, #39 is a good one:Eat all the junk food you want as long as you cook it yourself. My add, within reason
10:51 AM - 29 Dec 2009
   
Google Books 
Time
Volume 175, Issues 1-12
2010
Pg. 148:
“I actually came up with a rule: Eat all the junk food you want as long as you cook it yourself. One reason we struggle with obesity today is that special-occasion foods like French fries, cakes and cookies have become so easy to obtain.”
 
Google Books
Make the Bread, Buy the Butter:
What You Should (and Shouldn’t!) Cook from Scratch to Save Time and Money
By Jennifer Reese
New York, NY: Free Press
2011
Pg. 108:
“Eat all the junk food you want as long as you cook it yourself,” Michael Pollan writes in Food Rules. “If you made all the french fries you ate, you would eat them much less often, if only because they’re so much work. The same holds true for fried chicken, chips, cakes, pies, and ice cream. Enjoy these treats as often as you’re willing to prepare them—chances are good it won’t be every day.”
 
Oh, Michael Pollan, you underestimate me.
 
Twitter
Easy Cooking Guide
‏@EasyCookGuide
Eat all the junk food you want as long as you cook it yourself. - Michael Pollan http://www.easycookingguide.com
11:05 PM - 20 Jan 2017