When it comes to insecurities that are justified, I was obese, so I do have some experience. Words wouldn’t have helped much, but actions would. When you have some kind of unappealing trait, people recoil from you. They won’t look at you, they won’t touch you, they just try to disappear from your general vicinity. Just being there and giving off the vibe that you are comfortable and happy being with me would have made all the difference.
Also worth noting that its worth being careful what you say, even positive.
Like, when you’re obese, you know it and you probably hate it. At the same time, as was said, it feels like everyone is disgusted by your existance. For that reason, drawing attention to it in general can be othering. For example, being told “good for you” for ordering a salad or going to the gym wasn’t a rare occurrence in my experience, and while positive on the surface, is just insulting and patronising.
Also, for the same reason, don’t try to be their doctor or therapist. There is likely any number of underlaying issues that maintain the obesity, be it trauma, mental health disorders (including many seemingly unrelated to eating, like depression or OCD), insulin resistance, diabetes, ect. ect. ect. People (and their doctors) know their own health history better than you do. Odds are, you’re either going to be telling them something they already know for the millionth time, or even giving bad advice that can make it worse - esspecially as it relates to mental disorders.
If you want to help, don’t be patronizing, don’t try to replace their doctor, just treat them like you would anyone else.