I have a hard time believing that you have 13% body fat. I am 6' tall and weigh the same as you do and after all my cycling, I have enormous leg muscles from all my cycling. So the first thing to check is is your fat measure reasonably accurate? I am not saying that your figures are wrong, but they could be. But that would mean you would have a whole bunch of muscle for someone your size.

Now the thing is, you seem to think that you can lose 100% of your body fat. If you did that, you would kill yourself. Fats make up our cell membranes (phospholipids). No fat, no membranes. Also fats do things like cushion certain organs and parts of your body. For men, 4% body fat is just about the lower limit that can be achieved. Body builders and wrestlers do this and they can tell you that 4% body fat is hard to reach and hard to maintain. It really isn't worth doing for the average guy. I would think a comfortable lower limit for most people would be 8-10%.