The debate over how much carbs and fat runners need to enhance their performance is both enduring and trendy. Current carb-bashers claim training your body to burn more fat is a more effective way to sustain effort. But a new study published in the Journal of Applied Physiology undermines that theory.
Researchers at the Australian Catholic University’s Mary Mackillop Institute for Health Research investigated how the body uses carbohydrate and fat sources during high-intensity, extended running. Researchers looked at 12 competitive male runners in four trials, randomised in order, in which participants ran on a treadmill at a speed of 95 percent of their best half marathon time until exhaustion.
In each trial, participants consumed a pre-exercise meal with different nutritional values. Participants in trials one and two were fed carbohydrates in the form of jelly. Participants in trials three and four fasted overnight and were given a jelly that looked and tasted similar to the carb group but contained no calories. In order to test whether blocking the use of fat as fuel hampered run performance, participants in trials two and four were given nicotinic acid, which prevented the use of fat stores during the test runs.
The study found that carbohydrates were the primary fuel (83 to 91 percent) used during all of the run trials. The nicotinic acid did not impact the runner’s performance or the body’s ability to use carbohydrates as fuel. While the body used a small amount of fat for fuel, the number one source was carbohydrates.
Bottom line: Carbs are the primary fuel for running at half marathon race pace. While some are experimenting with fat as fuel, runners should focus on packing their carbohydrate stores prior to endurance events.
Carb-load the right way
Keep your base diet stocked with quality carbs: Aim for several daily servings of whole grains, such as black rice, quinoa and farro. Include starchy veggies like sweet potatoes and corn as well.
Refuel with carbs: Long runs demand a restocking of glycogen stores, so aim for 75 to 100 grams of quality carbs postrun, along with 20-25 grams of protein. A turkey sandwich on hearty 100 percent whole grain bread, stuffed with plenty of vegetables and a serving of fruit salad will do the trick.
Prior to race day, balance calories in with tapered training: Filling up your glycogen stores requires a full 48 hours and an ample intake of carbs, but “overstuffing” may leave you feeling sluggish. As you dial down on your training, cut back slightly on calorie intake while watching diet quality (leave out foods high in sugar and fat).
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