Gaining

There's a theory that eating more protein will add weight to your ass and sugary foods will add to your boobs but I don't know how true that actually is in practice. If the sugary thing is true, that would definitely be true in my case

The only info I have heard about that kind of relates to this is high sugar and carbs tend to cause more visceral fat gain. Which is the so-called bad fat that can lead to health issues. It's the kind that causes the tight beer belly look.
Then there is subcutaneous fat. Which is the kind right below the skin. The soft jiggly kind. It doesn't contribute to health issues as much as the other kind of fat. Eating and drinking fats, like in dairy is supposed to help with subcutaneous fat and reduce visceral.
I would think subcutaneous fat would be what you would want. As the areas you want to gain in would seem to be areas where subcutaneous fat would be stored. Having said all that, at the end of the day your genetics has the final say in where you gain. Best of luck!

I'd say all of that is dead on from what I've learned, too. The one thing I want to add is that you cannot control where that subcutaneous fat goes -- that seems to come down to a mix of genetics and hormones (which themselves are somewhat genetically influenced). LOTS of people wish there was a way to control this, but I've never seen any credible information that it is actually possible.

Protein helps build muscle, and we have a lot of muscle in our asses. 😁😜 I wonder if that's where this came from? Genetics usually rule where subcutaneous fat goes, but gaining butt muscle can contribute to a rounder shape.