Confusion over anorexic sibling

Hi. My sibling is overcoming an eating disorder at the moment, going through recovery to gain weight and get better mentally.

I'm just confused, and sorry if this is a bit gross... I was under the impression that people with anorexia are usually constipated, but my sibling is always gassy/going through numerous bowel movements a day. Is this normal? I'm so confused.

They've just gone from eating basically nothing to now eating 'normally' (three meals three snacks i think) and having a LOT of bowel movements. is it just because they're being exposed to more food than they're used to, or is it a medical problem?? Idk I'm confused and I spend half my nights awake, wondering if they're going to be okay or not, and everything they do worries me right now.

Thanks.