“To feel ‘fit as a fiddle,’ you must tone down your middle”

“To feel ‘fit as a fiddle,’ you must tone down your middle” is a saying that has appeared on many lists of dieting and exercise quotations (where it is usually credited to “anonymous”). A fiddle is an instrument with a thin middle; the sayings “fine as a fiddle” and “fit as a fiddle” date to at least the 1600s.
 
“To feel fit as a fiddle, you must tone down your middle” has been cited in print since at least 1987, when it was listed in ‘Words of Wisdom” by the group TOPS (Taking Off Pounds Sensibly).
 
   
(Oxford English Dictionary)
as fine as a fiddle = as fit as a fiddle.
as fit as a fiddle: in good ‘form’ or condition.
1603 tr. Batchelars Banquet iii. sig. C2v,  Then comes downe mistresse Nurse as fine as a farthing fiddle, in her petticoate and kertle.
a1605 W. Haughton English-men for my Money (1616) sig. Gv,  This is excellent ynfayth, as fit as a Fiddle.
a1605 W. Haughton English-men for my Money (1616) sig. K3v,  This is excellent, this is as fine as a Fiddle.
 
21 May 1987, Duncanville (TX) Suburban, ‘Tuesday Evening TOPS” (Taking Off Pounds Sensibly), pg. B3, col. 2:
Words of Wisdom:
(...)
2. To feel fit as a fiddle, you must tone down your middle.
     
Google Groups: news.admin.net-abuse,sightings
20040211-spam
Feb 11 2004
(...)
To feel ‘‘fit as a fiddle’’ you must tone down your middle.
 
Google Books
How the Rich Get Thin:
Park Avenue’s Top Diet Doctor Reveals the Secrets to Losing Weight and Feeling Great
By Jana Klauer
New York, NY: St. Martin’s Press
2006
Pg. ?:
To be “fit as a fiddle,” you must tone up your middle.
 
Google Books 
Chicken Soup for the Soul:
Shaping the New You: 101 Encouraging Stories about dieting and fitness—and finding what works for you
By Jack Canfield, Mark Victor Hansen and Amy Newmark
Cos Cob, CT: Chicken Soup for the Soul Pub.
2010
Pg. 72:
To feel “fit as a fiddle,” you must tone down your middle. ~Anonymous
   
Google Books
Physical Activity & Health:
An interactive approach
By Jerome Edward Kotecki and David Q. Thomas
Sudbury, MA: Jones & Bartlett Learning
2011
Pg 160:
To feel “fit as a fiddle,” you must tone down your middle. —Unknown