A very interesting study (you can read the whole article for free, not just an abstract) on the effects of a pre-exercise high-fat meal (HFM) on endurance performance versus a high-carbohydrate meal (HCM).

We observed that the time until exhaustion was significantly longer in the HFM + M (p 0.05) than in HFM + P and HCM + P conditions. Furthermore, the total amount of fat oxidation during exercise was significantly higher in HFM + M and HFM + P than in HCM + P (p 0.05). These results suggest that ingestion of a HFM prior to exercise is more favorable for endurance performance than HCM. In addition, HFM and maltodextrin ingestion following 3 days of carbohydrate loading enhances endurance running performance.
— Significant Effect of a Pre-Exercise High-Fat Meal after a 3-Day High-Carbohydrate Diet on Endurance Performance

This study puts some scientific backing to my own findings now I've switched to a predominantly high-fat low-carb diet. Interestingly, I've not tried the maltodextrin jelly part yet. Maybe before my next race.