The sugar in fruit juices is predominantly fructose, which is a disaccharide, meaning that it contains two molecules of glucose joined together and must be bro-ken down to glucose in order to be absorbed, which may cause a delayed or muted effect on the blood sugar. Fruit juices will also contain a moderate amount of some vitamins and minerals.
Sodas do not contain significant amounts of vitamins or minerals. The sugar in regular non-diet sodas is glucose, which is very readily absorbed and sweeter tasting. The amount of sugar in a standard 12-ounce can of regular soda is equivalent to about 9 teaspoons of table sugar (which is neither glucose nor fructose, but sucrose, another disaccharide) and therefore provides a large amount of calories, which can raise the blood sugar level very quickly.
This is helpful if a low blood sugar reaction is being treated, but not a recommended part of the diabetic diet, as it causes a very sharp rise in blood glucose to levels above those recommended. This rise is hard to prevent with either pills or insulin, without giving doses that will later lead to low blood sugar levels.