I wrote a(n overly) lengthy response to a different reply, but basically, the human body can tune itself to be more or less efficient with its calories dependin

I wrote a(n overly) lengthy response to a different reply, but basically, the human body can tune itself to be more or less efficient with its calories depending on how much of a surplus it thinks it has. The very simple explanation is that human waste has a non-zero calorie content, and can be higher or lower depending on how interested your body is in extracting every last calorie from your food. This is of course without getting into satiety and the challenges of people society considers too fat being expected to just be hungry all the time, or the actual science showing that dieting is far more harmful for your body than being "overweight", just a very simple explanation for why calories in and calories out aren't as useful of a measure as everyone (including me, by the way) would love for them to be.