| well....
I have to try very hard not to get on my high horse, but my personal view is that there isn't a great deal of difference between a simple sugar and complex carbohydrate.
it's one of those diet advice things when everyone believed that glycemic index of foods was important. The idea is that by eating complex carbohydrates instead of sugars, you would slow down the rate at which glucose would enter the blood stream, would need less of an insulin peak, and therefore would be healthier. And this is all fine and dandy, except that this model is far far too simple to represent what actually occurs during digestion.
First off you need to know what a complex carbohydrate is. There are plenty of them, but really the only complex carbohydrate that is relevant is starch.
starch and glycogen are almost identical in chemical structure, they just differ in shape. Starch is composed of long chains of glucose molecules known as amylose, which is bound to blobs of glucose known as amylopectin.
rest assured that free starch is broken down extremely quickly by the body - astonishingly the starch from a boiled russet burbank potato can enter the blood stream faster, than glucose dissolved in water.
simple sugars are just that - there are only 3 molecules worth worrying about - glucose, fructose, and galactose - simple sugars are made by combining them together in short chains -usually bimolecular structures.
so you have sucrose - simple table sugar is a composed of glucose bound to fructose., maltose is 2 glucose molecules bound together and lactose is glucose and galactose bound together.
fructose (of which there is much angst) is turned into either glucose or fat. What it gets turned into depends largely on available glucose in the liver.
the point is when you eat carbs be they complex or simple, then their ultimate fate is to get turned into glucose. Any excess is turned into fat.
my personal view is that the distinction is purely artificial. what actually matters most to you is how fast they get there. so...
fat slows down the absorption of carbs including simple ones - which is why ice cream typically has a medium GI (it's significantly less than mashed potato)
Another handy guide is the degree of processing the food has undergone - the more processing then the more easily nutrients are absorbed - apples have a lower GI, than juice for example.  | 
