Speaking for a friend, he'd be absolutely overjoyed.
On one level, anyways.
Speaking for myself, I'd be curious as to why. If I had a girlfriend, I'd expect a good answer from her. I'd also ask if she suddenly lost 30 lbs, stopped showering often and watching movies and started going to the gym daily. Point being that drastic change has motivation behind it, and I'd like to know what it is.