Also to OP, no we are not gonna say the word "all" but
1) YES. EDs (Eating Disorders) ARE real and they can be really DEADLY. Anorexia, bulimia (I am still 3 years recovering from that BTW), pica (do not have that anymore thanks to treating anemia) and just to acknowledge any kind of EDNOS are very long term and dangerous to live!!
2) Just because fat shaming worked for you does NOT mean it is likely to work on others! It is VERY well known to cause EDs!
Your body when struggling with these disorders will be used to habits that you will struggle to get out of because of many things that you yourself may think about, like how other people see you (maybe you wanna be as thin/big as your crush, or you're thinking about future events you want to look good for each time, etc.) and what they're gonna say ("you've slimmed down!" "You've gotten wider!").
And sometimes, even if you're not thinking about ANY of that, since your body still has those unhealthy habits imbedded to it, it will seriously do it's best to force the habits upon you or worse cause terrible symptoms (insomnia, coldness, prone to diseases, mood swings, breakdowns, etc.), which can cause just as more risk as obesity to many.
Eating disorders do NOT discriminate. If you or anybody you know has one please help them and reference healthier habits with food, whether they are underweight or obese, be careful as to how you approach the topic and PLEASE be considerate. It is NOT a simple topic to speak of especially with someone who already constantly thinks about it!! Please remember that.