is the key. Insulin sensitivity and control plays a role, but carbs don't make you fat alone.
Read this blogpost today from lean gains (shirtless dude alert. I guess that makes it's not w/f/s): http://leangains.blogspot.com/
And for the record, I tend to be more of a low carb leaning person (certainly not high carb).
What are your numbers like in terms of height, weight, body comp. and training?