Seriously, in writing (and in real life) DO NOT DO THAT. You could maybe use an exception for focusing on one trait or marking if it becomes a plot point or a smoking gun, something important (like Potter's scar, which was still mentioned less in the series that the weight of the main character in this singular novel).
When you write for a body type (any) don't dig up overused adjectives, and for the love of everything, don't continually mention it.
In literature, as in life, weight is one detail. One. I tend to mention it once when writing a character, maybe twice, but usually just that once. First, it keeps from barraging the reader while they are painting the picture of your characters in their own mind, and secondly, once again, it is one detail and not generally made to make or break an entire image or convey anything else. When you use it that way, it often reads as unimaginative.
Listen, being fat isn't easy. I mean I have been overweight from birth. It never got better, or easier. The worst part about it is always the abuse. We're not represented well or often, and when we are, whoever was brave enough to try it is demonized for treating fat people like human beings. I guess we are supposed to be continually ashamed until we're thin. That has never worked, and studies show that the abuse of overweight people actively hurts them, but hey, maybe they are only trying the shaming thing because that is all they could come up with...
And that is why body type in literature (and the ability not to focus on just that in character building) matters. It fleshes out your world, and if you do it right, the real world.
Nobody has to like or love your body type. And you can write for characters with any body type you wish-thin, fat, in between- hell, create a character with NO BODY (those are fun).
Honestly, the only time it becomes an issue is when somebody who doesn't like a trait about you rails against your right to exist.
Nobody has that authority. Nobody. You can prefer green-eyed people over those with blue eyes, but you can not discriminate, abuse, or call into question the worth of a person with blue eyes. That's literally the only line. That's it. You can dislike anything you want, without owing an explanation. And that is 100% your's, and you can own it in your fiction, too.
Just don't hurt other people for what they look like.
You would think we'd be better at this by now.
That's a really, really simple concept.
For those of you writing for bodies of all shapes and sizes compassionately and well, thank you. I'm hoping to pass onto my children the idea that we are all more than a number on the scale, and when more fiction supports that, it will make a big difference.