How does blood glucose breakdown related to body fat percentage?

It doesn't : There is no direct correlation.

Not really, but....: If you utilize a significant portion of your blood glucose, your body will first break down rapidly available carbohydrate to manufacture new glucose. When that is exhausted, it will begin to metabolize fat to provide more nutrition. I suppose that would very slightly lower your body fat percentage, but it would be imperceptible. For all practical purposes, there is no relationship between the two.