This is just not true. As a counterpoint, I have done 48 hour wakeful crunch time sessions before with very little eating (about 400-800 kcal/day). I typically

This is just not true. As a counterpoint, I have done 48 hour wakeful crunch time sessions before with very little eating (about 400-800 kcal/day). I typically lost 5 lbs over that time (which I mostly gained back as much of it was water, but also lost some fat and muscle). Don’t extrapolate your anecdotal personal data like that. Your weight is mostly a function of how much stuff is in your bowels, glycogen, how hydrated you are (indirectly how much salt you have), your muscle mass, fat mass, and then a relatively static amount for the rest (organs, skeleton). Sleeping does not magically make you lose weight. You just lose a lot of water while you sleep due to breathing, and might lose a small amount of fat and/or glycogen