It's probably not as simple as just the fiber in fruits protecting against fructose/glucose, but it does help. (EDIT: what I mean is, don't replace fruits with a glass of metamucil and sugar :))
Soluble fiber is just that: soluble in water. In your stomach, it absorbs water and turns into a sort of carb-trapping gel. While the carbs are still eventually digested, the gel slows down the absorption. This is good, because it helps to regulate your blood sugar (not as much of a big spike and drop).
Since blood sugar spikes == insulin response == hungry signals, this is quite useful.
Insoluble fiber is also useful, but mostly just for waste processing.
Soluble fiber is just that: soluble in water. In your stomach, it absorbs water and turns into a sort of carb-trapping gel. While the carbs are still eventually digested, the gel slows down the absorption. This is good, because it helps to regulate your blood sugar (not as much of a big spike and drop).
Since blood sugar spikes == insulin response == hungry signals, this is quite useful.
Insoluble fiber is also useful, but mostly just for waste processing.