GU claims to have an 80% Maltodextrin (complex) to 20% Fructose (simple) Carbohydrate buildup in their 100 calorie serving pack.

Hammer Claims that their 90 calorie ounce contains 23 grams of complex carb's and only 2 grams of sugars and no fructose! They only use Maltodextrin and real fruit concentrate.

this is copied from Wikipedia and talks about many peoples concerns with consuming fructose:
Excess fructose consumption has been hypothesized to possibly cause insulin resistance, obesity,[2] elevated LDL cholesterol and triglycerides, leading to metabolic syndrome. Short term tests, lack of dietary control, and lack of a non-fructose consuming control group are all confounding factors in human experiments. However, there are now a number of reports showing correlation of fructose consumption to obesity,[3][4] especially central obesity which is generally regarded as the most dangerous type.
http://en.wikipedia.org/wiki/Fructose