I’m wondering if character weight can increase in your game? Right now my Zoe keeps losing weight constantly, and very significantly at that, even though she doesn’t exercise. And if she does exercise, she loses weight many times faster until she becomes skinny. I have to periodically use cheats to modify the character to restore her weight.
My characters are constantly losing weight too. All my characters eventually turn into skinny little mosquitoes, or rather, into mosquito skeletons.
I wonder how long ago this started? I suspect this bug in the game has been around for a while 
It feels like that was a very long time ago. I remember that as soon as the Cahaya expansion came out, I moved a girl there, and she would gain weight if she ate more than she should. I even bought her a weight loss pill. But the second generation only lost weight, and the third one did too.
Mine are constantly losing weight too. Just like @LeeLoo said, I think it started to become really obvious after the major update right after Cahaya. Eating one of the donuts for instant weight gain helps, but then they gain a little too much weight right away, so this shouldn’t be a constant solution.
It happens to me too, but then men gain weight at the slightest thing.
Wow, that happened so long ago
were there any reports about this bug from players? It seems like we should flag this as a bug, since it’s happening to many people (or maybe everyone, they just don’t all notice it) and it’s been going on for such a long time
It’s been reported throughout numerous updates, if I remember correctly. Here’s one of those more recent threads if you’d like to support it to increase attention: [0.8.5] Zoi lose all their weight and become super thin/skinny in a few days. 
I was also losing weight. I used to track calories through donuts since I was constantly doing sports 24 hours a day, I didn’t pay attention to it, but at one point I got tired of it and turned off the function.
Looks like I’ll have to turn it off too until the developers fix it