You need to do high gi's on a carb-up, the main point of a carb-up is to restore leptin levels so that your metabolism is back on track for another week of intense workout and caloric deficit eating. Leptin levels get raised by a influx of calories and such, and the best way to go about loading yourself up with calories is via carbohydrates, Leptin responds better to high gi carbs which is why you want to do this at the beginning of your carb-up, and to reduce the risk of storing large amounts of water/fat at the end of the carb-up, you switch to low-gi carbs which do not spike your insulin as much as high gi's do! But you need the high gi carbs. I always get a bit frustrated and confused because I learned all my low-carb stuff from a bodybuilding forum. I'm not a body builder, I have nice muscle tone, but not bulging muscles, anyway, there is a lot to be learned from their methods, and from what I learned on the bodybuilding boards is you need to restore leptin levels as you get leaner. Some bodybuilders carb-up every 2 days or every other day!