Most runners are well aware of the benefits of being properly fueled for a run of any distance. In fact, "hitting the wall" is often attributed to simply running out of glycogen supplies.
But scientific research has established that fasted training (training with low blood glycogen levels) can lead to favorable adaptations in the optimization of fat as a fuel source. Since fat stores are much more plentiful in the body than glycogen supplies, training your body to favor fat over glycogen seems to be a smart training strategy, especially since burning fat is a popular goal for runners.
Unfortunately, fasted running is a strategy that can be difficult to nail down for age group athletes. In fact, if done improperly, running with your glycogen stores on empty can result in low-quality training that winds up hurting performance. If you're going to attempt this training approach, there are a couple of smart ways to use fasted training to burn more fat and improve your race-day performance.
Timing is Everything
The first strategy you might consider is one elites have been using for decades. Evidence supporting diet periodization was published as early as 1995 in the Journal of Sports Medicine and has been bolstered by a number of other studies since. Here's how it works:
—Eat a moderate- to high-carb diet in the early weeks leading up to your race.
—10 to 17 days before the race (at the beginning or midpoint of your mileage taper) switch to a high-fat/low-carb diet for one to two weeks.
—Three days before your race, switch back to a high-carb diet. Make sure to eat a high-carb meal the night before or morning of your race.
Following this dietary periodization schedule allows your body to make the metabolic adaptations to better utilize fat, but also ensures you won't bonk during your race due to depleted glycogen stores.