I just got done studying muscle kinesthesiology as it relates to endurance. If you are working at a lower heart rate, like 60%-70%, your body can fuel itself from fats. But, you still must have carbs to assist this conversion. "Fat burns in a carbohydrate flame" according to Covert Bailey.

If you're working at a higher heart rate, you'll need simple carbs. Malodextrin is one of the best & usually one of the first ingredients in Cytomax and other drinks of that type. As stated, fructose is harder to break down. The glycogen is needed keeps your muscles contracting. It isn't stored as fat unless you ingest too much.

Also, consider the EPOC effect after very long or interval rides. Your body will continue to burn calories to mend the small muscle tears and replace muscle glycogen. The amount of EPOC is directly proportional to the difficulty of the ride. That's why you need to fuel your muscles immediately after a ride if you intend to do it again soon (before 48 hours.) You'll recover quicker if you have a liquid with a protein:carb ratio of 1:4. You want to avoid fats because fat will delay gastric emptying, thus your muscles will not be able to quickly absorb the protein & carbs they crave.

Your mileage may vary. You can train your body to burn fat at a higher heart rate but it takes time. The fact that some people do better with fats & protein on their rides shows how different we are (but, I'll bet a little simple carbs would supercharge their ride. )