There are foods that are naturally high in dextrose though I can't think of many off hand. I think smarties are high in dextrose as are sweet tarts. I remember some TKD guys raving about them. I've found some non-fat ice cream, which I currently use post workout, that is high in maltodextrin. Only thing I'm not sure is if the maltodextrin is used for filler or sweetness. At any rate as long as you're not getting fructose I think most other sugars do just fine. Some cereals like corn flakes have a higher GI rating than dextrose so just do some research. While dieting I like to eat as much real food as possible so getting that many carbs in shake form is a waste to me. While bulking it's fine since you're pounding down the food and probably need an easy way to get calories.