My sister is 150 pounds over weight...

She just recently went to the dr for a physical and the dr came back and told her she was obese and about 150 pounds over weight. She was very upset about this, obviously, but instead of being upset and working on losing weight, she took the opposite approach. Shes just complaining about how wrong the drs are about BMIs and that them telling her she's obese will cause eating disorders. I understand that BMI can be very inaccurate if you are an athlete, but thats not the point. The point is she is 150 pounds overweight and I am very worried about her health. Not only her weight problem, but her mental health as well. Her confidence has been so low the past 4 years and I feel like if she were to lose some weight, it would help her physical AND mental health. I just don't know how to help her... I have always been a healthy weight and never really battled with it... I dont want to come across as rude or "be like me"... she's a beautiful woman I am just scared about her health!!! How do I approach her about it without coming across as mean? I really am concerned...