"I get what you're trying to say and some of what you're feeling when you say triggering phrases but, for me, it's making me compare my weight to yours. I know that you're not making any comment on me and that this is my problem but I would really appreciate it if you could express yourself without using the words X and Y. If that's not possible, I may need to excuse myself sometimes when these topics come up for my own wellbeing. I wish I could be a person who could fully listen without my own issues clouding things but that's not where I am. Please know that if you're ever really struggling that I am here for you. I love you and I don't want something like this to impact our friendship."

How does that invalidate the friends issues or feelings?