Co-fucking-signed, thank you. My mother says she has a policy of never commenting on weight loss, because there's always the chance that the answer to "what did you do?" will be "chemo". There are many, many reasons someone could have lost a lot of weight in a short period, some of them coming from deliberate choices and some of them really not, and even leaving aside the issue of body-policing, it's just freaking rude, because there's every chance the cause might be something they don't particularly want to talk about.

(For that matter, being constantly told "what the hell is wrong with you? You're too skinny, eat something!" by friends was not really helpful when my ED was at its most intense. Shaming me for starving myself down to weight in the double digits: a completely effective solution to countering the body-shaming society at large was giving me for not looking like that! In no way would it leave me with the conclusion that no matter what I did my body was disgusting and worthless and I could not possibly win. Even when the reason someone is super-skinny actually is ED rather than the many many other things that could have weight loss as a side effect, more body-shaming is not helpful.)