Actually, obesity does not actually cause heart disease and diabetes. Heart disease is largely heritable, and diabetes risk for the obese is only 6-8%. And in diabetes, weight gain may be a part of the disease. It was certainly true, for a diabetic client of mine, that she gained weight precipitously around the time she was diagnosed.
And on the obesity thread, I posted links showing that obesity seems to confer a certain level of immunity for heart disease and diabetes.
Screwy, I know, but that's what the research is telling us.