At the present there are no "visual" changes to the NPCs (except some pregnancies). Not sure if there ever will be, since all images have to be rendered individually.
I have an NPC (Astrid actually) that need to be on 1 ration a day to not go very fat.
You might want to give the game "Kenshi" a look. I love the game, even though the graphics are a little bit old by now. But it's real time 3D and you can "shape" NPCs from very skinny (from passed out starving actually) to well fed to super buff and muscular. But no "fat" body types. I don't think there are mods for "overweight" NPCs, but given that Kenshi has a huge mod community, I wouldn't be overly surprised too. Actually, if you take the "sex" part aside, it's got a lot of common ground with Masters of Raana, depending on how you play it. Kenshi doesn't exactly have a story. It has stories and NPCs with their own stories but ultimately, it's a huge sandbox with no rules at all.
There is a Kenshi 2 in the works, but might be a few years... all the dev says is "It's ready when it's ready". The original took 10 years (plus 2 years of "ideas") to be finished, but it's a masterpiece.