Being told that it threatens your life, and being told to diet, without being told how to do it successfully, can be enormously frustrating - doctors who don't understand this could improve by learning as much.

Agreed. I find the "how" immensely frustrating, and have tried many different methods. The only thing my doctor suggested as a way to lose weight was to try to exercise at least three times a week. She said that I should do research on diets and nutrition, or go to a nutritionalist, to find out what the best eating program is for me. My current diet is pretty common sense, actually; I *really* needed to cut down on my portion sizes. That's helped me a great deal.