All of this. One of the reasons I started this tumblr like a trillion years ago is because I went through a period in my later adolescence and young adulthood where I lost a bunch of weight due to an eating disorder and exercise bulimia and I was treated vastly, vastly better.
@lisadabahdest is absolutely correct in all her observations. Not only did I have way more friendship and romantic opportunities, I also had way more people wanting to give me jobs, acting opportunities, and mentor me academically and artistically.
Worst of all and utterly heartbreaking was when one of my parents treated me vastly, vastly better when I was thin than before. This parent was also fat and hated that about themselves, and totally projected this vicarious triumph over fatness on me. Suddenly this parent, who was never interested in anything I did or accomplished, was bragging to me to all their friends, bringing me up in conversations, wanting to hang out and talk with me, etc etc.
When I recovered from my eating disorder and gained a bunch of weight, this parent started treating me like I didn't exist anymore. Thank goodness I had another parent who didn't treat me differently at all, except that they were relieved and happy I was doing better and was more healthy (even though I was very much larger).
I will never not believe there is thin privilege and fat discrimination, because I lived that experience. I was my own natural experiment. And I will always believe fat people when they talk about the discrimination we face, how society ices us out, how people are trained as little kids by parents, teachers, doctors and even fucking cartoons to be disgusted by fat people and to dehumanize us.
Share the shit out of these natural experiments. We are silenced, gaslit, told that our experiences aren't the norm and don't prove anything. But people who have lived as both thin and fat will tell you the same thing if they're being honest, and there are a lot of us.