People always will say things and not in positive way, you have to be prepared for that, if you willing to become fat. I was very skinny and started to gained weight only recently, after years of efforts. Like what Ditzy said, it takes years of eating to really transform your body, from a skinny one to really fat. Most of my friends did not say anything about my new weight (Women at work just feels more comfortable to offer me snacks 😸). It's family that usually comments on the issue, in my case. So, eat up, take a decision (whatever it's to gain weight or not, it up to you), and after that do whatever you can to become fat, real friends will not leave you because of that, and you always will have a new ones. Don't let people stop you from doing things. It's your life, not theirs.
4 years