There are HUGE differences between 'white foods', ie, white rice/table sugar(sucrose) and things made with sucrose like white bread. Everything made with sugar(sucrose) has a carb profile of 50% FRUCTOSE and 50%glucose. Sucrose, white bread/bagels/etc have more in common with High Fructose Corn Syrup than with white rice or potato.
All you ever wanted to know about fructose metabolism: http://www.youtube.com/watch?v=dBnniua6-oM
White Rice and White Potato have very little sugar(ill get to it). White rice in fact has only 1/10th of one gram of sugar per cup. Imagine that. It does however have starch. And the starch is broken down by the human body into glucose. But notice, its not broken down into fructose.
There is a huge difference and if you are thinking about adding more 'carbs' into your diet, please do yourself the favor and add in carbs that enter the body as glucose and not fructose.