How can I tell my daughter that she needs to lose weight?

I’m a single mother of a beautiful 16-year-old daughter. Since the start of her teens, she has steadily gained weight and is now heavily overweight. I know the dangers associated with obesity, so I really want to help her get to a healthy weight. I’m just so worried that I will give her a complex and damage her self-esteem. So please tell me, how can I gently tell my daughter that she needs to lose weight? I really want to start her off with obesity therapy so she can live a healthier and happier life. Any advice is very welcome!