I don’t think I’ve ever heard carbo-loading. When did carb-loading come about?
There is a reference to “carbo-loading” from 1962, in Biology: The Web of Life VI, Parts [chapters?] 1-9, by Daniel D. Chiras, 1962, unknown page number (unknown due to snippet view limitations).
EDIT: on the 1962 date cited above, languagehat pointed out below that this was likely an error; it was:
...when I looked around at what I thought were unrelated databases, I noticed the publication date of 1962 re-affirmed. I see now that this was an error.
...Dan Chiras began his teaching career in 1976 after earning his Ph.D. in reproductive physiology from the University of Kansas Medical School, where he was awarded the Latimer Award for his research on ovarian physiology. That year, he accepted a teaching and research position at the University of Colorado, Denver…
-- biographical information for Dr. Chiras
I doubt that he would have published many textbooks on Biology fourteen years before that Ph.D.
also a reference in Yoga Journal, of July 1978, on page 38, in footnote #6 which cites an article by Roy Bruder, “Nature’s Carbo-Loading Secrets” by Roy Bruder, Runners World Magazine (Mountain View : World Publications, April 1978)
The earliest “carb-loading"s were seen from the early 1980’s, and were almost entirely snippet views or no-views. (This, from google’s dataset.)
“Carbo” short for “carbohydrate” and “carb” short for “carbo"--I speculate it came about as popular culture became more comfortable speaking of “chemical things.”