Is there a nice way to tell your girlfriend to lose some weight? Girls perspective needed!?

I've been with the same girl for four years, and we're likely to get engaged very soon! We've talked openly about getting married and have been planning our future together. We are very open about everything. I find her uncontrolably attractive, but I know that if she lost some weight she'd even be more breathtaking. I don't know if it's my place to even say this to her, but I'd support her if she wanted to. I don't know if she's thought about it or not, but she always talks about what great shape she used to be in (before I met her). I am interested to see what she'd look like if she got into that shape again! I am no schlub, I am 6'-6 and workout regularly. I can bench press 320lbs can run 3 mils easily, but I'm not a health freak. I am just health concious. Also, if I'm planning to spend my life with her, it'd be nice if she took better care of herself, so she stays healthy throughout her life. Is there a nice way to bring it up, or should I just let her handle it?