Originally Posted by
Bonzo Banana
I'm not sure what point you are trying to make but the body stores fat which is the perfect fuel for the body for times when no normal food is available. When the body is powered by its own stored fat not only is it the perfect fuel but your body is also not having to process food in the stomach. It's like running an engine on high octane fuel rather than low octane fuel plus making the vehicle considerably lighter with it.
High concentrations of sugar in natural food is rare and when the body encounters a source of such food like a fruit tree where the fruit may soon drop and spoil animals naturally go into a binge mentality to consume as much as possible for the short window when it is available to eat. Unfortunately that sugar binging is operating pretty much all the time with our modern diet.
https://www.youtube.com/user/drericberg123
If a person is gaining weight (fat or muscle) they're not in a calorie deficit.
People can build
some muscle in a calorie deficit, it's slow and not optimal, but it happens. But that muscle is physical stuff, it has to come from somewhere, your body can't just will new matter into existence. If it "comes from" stored fats, that doesn't change your weight any more than taking your wallet out of one pocket and putting it in another changes your net worth.