Hi Aussie, as we are not all the same you can only go by what you know affects you, the aspartame in coke may be the culprit, i haven't seen any favorable comments about it anywere, although i drink heaps of diet soft drinks including all the diet coke variations, it doesn't affect me in any way but i don't doubt i could affect others.
I did read somewere that caffeine could affect blood sugar levels, so i went caffeine free for a while but it didn't make one bit of differance to me either, but again that is only me.

Brian