The effect of exercise on boobs

I have a great girlfriend and I love her to death.  She's also quite funny--often without realizing it and I can rest assured that I'll be entertained for life.  One time she dropped this great nugget of knowledge and told me this: "If I start working out, you do realize that the first part of me to lose weight will be my boobs."  Screech.  I, in fact, did not know this.  This was news to my male brain.  Is this real or is it a hoax that she concocted in order to have a great excuse not to work out and simultaneously have my support in that choice to not work out?  I can't be sure, but I am sure that my first thought was, "would you like some ice cream?"