I want my friends to lose weight
Why do you want your friend to loose weight?
The distinction between why I want that is because I'm nice and also I don't want them to suffer.
You have a good heart to feel you should want that for your friend, but they can only help themselves. You can mention it casually but not critically, that will help them regain their common sense without feeling bullied about it. If you don't care about it then no one else will and they will gain more and more weight.
I don't care, they need to lose weight because I mean it.
Be a good friend and tell them your concern. If they are willing, help them to lose it, exercise with them and show them how to eat properly. Guide them to be more healthy and you'll both be in better shape.