>The vast majority of calories our bodies burn are upkeep related and this upkeep does not change significantly based on our diet.

Apparently it does if you went on too many yoyo diets. Look up reverse dieting to increase your sustaining calorie level again, it works in both directions. Its more or less the efficiency with which your metabolism functions

I liked Jeff Nippards Video with Eric Trexler on the topic https://www.youtube.com/watch?v=xiYJW9pViaM https://www.researchgate.net/profile/Eric-Trexler

From 2019