I come from the future, and we have two seasons now, plus an announced 'compilation film' coming.
Also, as a tall person, myself... Yes, I'm pretty sure I could eat two meat buns, as well. And my absurd tall person metabolism would make them vanish. Hell, I could probably eat three of them and barely notice it. Mmm, meat buns... been awhile since I've had some.
I seem to recall people claiming Anna might be on the edge of plump, but it's also quite possible she's got the same kind of 'tall person metabolism' that has always resulted in what my family called a 'hollow leg', because I'd eat a whole lot of shit and I'd never gain weight, as if it all went into a hollowed-out part of my anatomy. I kinda suspect Anna is the same way. The only reason she's so self-conscious about her weight is because she's heavy for her age... only because she's so damn tall for her age. I feel like she's always been depicted as pretty damn slender, outside of her hips/butt, thighs, and bust, which only accentuates her attractiveness.
Hell, just about every time that Miss Mangaka has shown us Anna in casual wear and such that exposes her belly, it seems to be very flat and lacking in fat. I'm probably on the money with her having 'tall person metabolism' that means she can eat just about anything and it's unlikely to show up. At least, until we get to a point of that being proven false, but I don't seem to recall that ever actually happening in the anime.