Strategic Carbohydrate Intake
A second strategy is a bit more complicated than the first, but the science supporting it has some pretty exciting results. A small study published in the April 2016 issue of Medicine & Science in Sports & Exercise split 21 trained athletes into two groups and had them each exercise twice a day for four days each week. The athletes in both groups, studied over a three-week period, consumed the same amount of carbohydrates (7g/kg of bodyweight per day), but the timing of their carbohydrate intake was different.
In the test group, athletes did not eat breakfast before heading out for a 60-minute low-intensity workout in the morning, then consumed all of their carbohydrates in the late morning and early afternoon, before completing a 40- to 50-minute high-intensity interval workout in the early evening. Following the high-intensity workout, the test group consumed a meal and a protein shake that contained no carbohydrates. The control group did the same workouts and ate the same relative amount of carbohydrates, but the carbs were consumed throughout the day.
At the end of the trial, the test group—which the scientists referred to as the "sleep low" group—shaved an average of nearly 50 seconds off their 10K run time, while the control group saw no improvement in performance at all.
In addition, the "sleep low" group lost nearly two pounds of fat, while the control group did not lose any fat, despite the fact that the total caloric and macronutrient content of their diets was essentially the same.
Quick Tip
When In Doubt, Take It Easy
Apart from caloric intake and composition, training intensity is the other factor that comes into play when considering the body's energy systems. Even in highly trained, fat-adapted athletes, glycogen is the preferred fuel source at intensities above 85 percent of VO2Max. In both of the strategies mentioned above, the workouts done in the fasted state were relatively low-intensity.
It's important that any kind of high-intensity speedwork be done under optimal fuel conditions (carb loaded) in order to get the most from those runs. Easy runs and long, slow runs lasting up to two hours are ideal for reaping the physiological benefits of fasted training. If you want to train your mental stamina as well, you can simulate the late stage of a marathon by adding a short (20 to 30 minutes) segment at tempo pace onto the end of a longer run in the fasted state.
By correctly manipulating meal composition, meal timing and training intensity, it appears that runners can effectively use dietary strategies to enhance running performance. As always, be sure to consult with your physician before you make any serious changes to your diet.
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