Keeping your boobs when losing weight? (One for the girls!)

I really hope I don't lose too much on mine. I'm a double G cup at the moment, but I hope I don't go down smaller than a DD. I've had big boobs all my life. It would feel wierd not to have anything there. I've read that if we do some strenthening exercises, it can help keep their size, but I can't remember where I read it. I must track down that article again.