I know that steroids and schitzophrenia medication have side effects that cause weight gain. I’m curious if the substances in these medications affect some people more than others.
This stems from the observation that even people who gained a lot of weight were typically overweight from a young age- childhood obesity seems to make the body prone to go on a runaway path of weight gain.
However, (anecdotally) I do not see people who were rail-thin at some point in their adulthood end up superobese. Anorexics, for example- even when they recover and eat normally, they seem to stay really really thin. Then again, it could be conformation bias.
So are there ‘barriers’ to weight gain beyond just the obvious calories in/calories out? For some people it is really difficult to lose weight; but does this also apply in reverse? Would a naturally underweight person stay thin even if on medication that causes weight gain, or say if they developed PCOS (in women)?