That should read “fictional overweight people,” but “fat” works better for the title’s rhythm. Also it’s fewer letters and some sites are weird about title length.

Anyway:

The problem that bugs me lately is overweight people in fiction. Specifically, the problem is how they are sometimes handled in fiction.

There are the obvious problems: the overweight person is treated like a slob, or lazy, or greedy, or any number of other reasons that translate to “they’re overweight because they can be,” and is usually the villain, while the hero has this super thin supermodel figure because of whatever reason.
Or the reverse, perhaps the thin person is sickly and the overweight person is considered “normal” by society’s standards.
The time the story is set besides the point, neither of these portrayals are particularly realistic, but that isn’t even the problem I have right now. No, my problem stems from the fact that authors need to point out the characters’ weight at all.

It’s fine if your story happens to include characters who are overweight; this, as I unfortunately know from personal experience, reflects reality.
It is just as fine to not include overweight characters, provided you either simply don’t call attention to it (that is, you never actually claim that none of the characters are overweight), or you have a good in-story reason for not including them (such as a dystopia in which everybody is starving… though even then, glandular disorders can still realistically create overweight characters).

It is fine to have a particular character fixate on their weight, if you are establishing this character as having an eating disorder, an odd personality quirk, or is just really into eating healthy… perhaps, in the last case, they have a family history of certain health problems and are trying too hard to offset that history.
It is fine to have a character fixate on their weight if you are establishing something about the world they live in, whether it’s that society’s definition of “beauty,” or some magical influence in which casting spells is as much a workout as running ten miles.

It is fine, even preferable, to have a considerable variety of characters and an equal variety of their reasons for their figures, just as you would with any other trait.

All of this is perfectly fine… provided you never actually mention a number or any other specific details.
Because once you start giving the reader specifics, you had best make sure those specifics are realistic. Otherwise you’ll find yourself offending a lot of people over what may well be an insignificant detail.

Do not, for instance, do not, give me a mother of three grown children who is lamenting the fact that she has to wear a size 12 as though only “fat” people wear something that big, unless you can give me a damn good reason the character should be unusually small.
Why? Because that isn’t fat!
Look, I have never been pregnant, so I don’t have that influencing my weight. I’m still in my thirties, so while I’m certainly not going to get younger, I should (theoretically) find it easier to lose my excess weight than someone in, say, their fifties. I have a medium frame… but I’m short.
Assuming I build some lean muscle and lose that excess fat, size 12 is right around what I should be wearing. I’m basing that, not on how big I’d like to be, not on what “seems normal,” but on how big my doctor says I ought to be.
But someone who has been pregnant, not once, but three times, is old enough for all three children to be fully grown, and gives not a single detail on her frame or height? Okay, so she “doesn’t think of herself as tall,” but she’s never claimed to be short, so I’m assuming she’s average for a woman. And since her frame isn’t mentioned either, I’ll assume medium. And she isn’t a runway model, nor a ballerina, nor an athlete, nor anything else that requires extreme attention to her weight. By all rights, she should be wearing a few sizes larger than me. Yet she with her size-12 “I wish I could still wear a size 8” attitude thinks she is fat.
And the only purpose this element served in the story is to show off that magical influence; she tires and sweats and yes, even loses weight, simply by casting what appear to be extremely simplistic spells in the form of songs. And even after another sorcerer had explained this effect to her, she still doesn’t understand how she is losing so much weight, and fears that she’ll eat enough to bloat back up because the spellcasting leaves her hungry all the time. There was nothing in the plot that required giving readers such a specific number….

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