a calorie whose source has little or no nutritional value: Junk food has only empty calories.
Origin of empty calorie
An Americanism dating back to 1965–70
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Food that has little or no nutritional value. For example, Snacking on beer and potato chips makes for a lot of empty calories. [1960s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.