This is very, very tough. I know you love your friend and don't want to lose her. But I have to tell you, anyone who is living in a big body already knows they are big. And they are very well aware of the many diets and "health programs" that promise a fix and don't deliver. And although there is science that links excess weight to heart disease, diabetes, and some cancers, you will have a hard time finding science (except for that sponsored by the multi-billion dollar diet industry) that shows causation, not correlation. Is the weight causing the disease? Or is she gaining weight because of the disease? If she is like the majority of Americans, she has tried to lose weight and either lost pounds on diets and gained them back and more or hasn't been able to stick to a "diet" and then binged in shame, making things worse.

In my opinion, the kindest thing you can do for your friend is be there for her and let her know that you are, no matter what. She will have to make her own way. If she does pass away, whether you say something or not, it will not be your fault if you said something or didn't say something because whatever you could say will have already been said by someone, be it a doctor, another friend, or a family member.