It's sad that so many health issues make weight gain almost inevitable but need you to stay slim in order to keep the issues manageable.
I have PCOS, weight gain is very easy, but being overweight also makes symptoms a million times worse!
My nan has arthritis - progressively gets harder to move and exercise, even harder when you're overweight.
My sister has depression and agoraphobia - depression medication made her gain a lot of weight very fast, which made the agoraphobia worse as she's scared of fat related judgement.
If there's a God, he's a little sadistic.