Oh, I am so here for this kind of thing (even if you just want to headcanon back and forth about this if no one picks it up!). Steve's helpless bewilderment is always my favourite part - say Bucky's half-starved when they're reunited, so Steve's going to be all about feeding Bucky up (expressing love through food is such a 1930s era kind of thing anyway) and maybe at first he thinks this is great, Bucky's looking healthier and taking comfort in something, he's even willing to go outside if pizza or Chinese is on offer - but it quickly becomes obvious Bucky isn't really enjoying his food, he's just obsessing over it, stuffing his face until his stomach hurts and swallowing without chewing enough.

And then he starts to get chubby and Steve doesn't really care about that part (he is pretty worried about how Bucky ate last night's lasagna steaming hot out of the pan, no way that didn't burn going down) but Bucky freaks and is all disgusted with himself and won't eat hardly anything no matter how Steve coaxes him with his old favourites. he's rationing himself to a little plain bread and dry cereal and his body just burns the fat off him until Steve finds him in the middle of the night scraping out the bottom of a peanut butter jar with his fingers, shuddering and hiding his face in shame, so of course Steve wants to find something good for him to eat but that's just the whole cycle again...(ahem, I may have a weird h/c kink for this)