I've noticed this in my own drawing style: there's no vocabulary within it for "fat" nor for any racial phenotype other than white. And solving that on the fly, mid-drawing, doesn't work so great. So far I've been copping out by not marking anybody, but as we all know, "unmarked" defaults to white and thin, especially when the characters aren't known to the viewer (which in my case, they're generally not). It's easy to justify that copping out with "Oh, just stick figures, which are almost by definition unmarked" but I've got two styles, and I notice that when faced with a character who has a "marked" body, I'll choose stick figures "just for today."

"Just today" has had a lot of days, so far. :-/