if you are a Atkins since june, you should be able to do the 28m without sugar.. You body is working just fine with fat and protein..

I am not sure what shape you are in, but if you go to the gym 5 times a week and do cardio, the 28m will be easy for you..

I ride every saturday and I do 40 miles at a good pace and including 4 killer hills we do it in less then 3 hours.. I eat a good dinner the night before, and something fatty (eggs and bacon) that morning and I am fine..