I moved into to Pro XC class at 148 lbs, and I was finishing nearly last every race. I put on 5 lbs. of muscle, and started riding farther and faster than I had ever done before.....and on the same 19lb. bike. So if you can lose fat and not muscle, that's great. If you're losing weight through muscle loss, I'd have to reiterate, I'll take the lighter bike.