Why? Can anyone explain?

So I'm pretty thin.
It goes like I eat A LOT, when I say a lot I mean A LOT and no, its not just me, my friends think that too. i eat a lot.
I gain weight, yes I do. Butttt, that weight doesn't showw. Like it is not noticeable that I gain weight. like woww? No shit, I want it to show. Why is it like this?
My friend weighs just 3 kgs more and looks a lot more obese compared to me, a vv huge difference.
Why? Can anyone explain?
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