I know you're sort of joking, but metabolism is extremely badly understood (most is not understood at all), and different people extract different amounts of ATP from food than others, that's just a verifiable fact. And eating less will make you lose weight, but how much less depends on, you guessed it, metabolism... So just saying "eat less" isn't very helpful IMO.

And it has not really anything close to do with thermodynamic laws, or you Had to have the emc2-gene for it to matter, thats all.

It's like relativity physics and car driving, it does intersect, but really not in any meaningful way.