The latest research suggests more fat burning does not necessarily equal better performance.
Written by: Matt Fitzgerald
It is largely taken for granted in endurance sports that anything an athlete can do to increase his or her capacity to burn fat during races is worth doing. The idea is that fat is effectively an unlimited energy source for exercise, whereas carbohydrate is limited and therefore limiting—use it up and you’re done for the day. So it makes sense for athletes training for longer races in which carbohydrate depletion is possible to conscientiously train in ways that promise to maximize fat-burning (hence carbohydrate-sparing) capacity.
How is this done? A traditional way to train to maximize fat-burning capacity is emphasizing moderate intensity in the training process, as peak fat burning occurs within the comfort zone of 65 to 75 percent of maximum heart rate. The more you train in this zone, the more powerful your muscles’ fat-burning machinery becomes. A newer method of increasing fat-burning capacity, which complements the traditional way, is withholding carbohydrate during long, moderate-intensity workouts. That is, instead of taking a sports drink along for your long run, you take only water. The body always burns carbs preferentially when they are made available during workouts. Withholding carbs therefore forces the muscles to rely more on fat for fuel than they would if a sports drink or energy gels were consumed, and presumably this enhances the workout’s beneficial effect on the athlete’s general fat-burning capacity.
However, a new scientific review authored by Louise Burke at the Australian Institute of Sport casts cold water on this practice and the related practice of training twice a day without replenishing carbohydrate stores between workouts, so that the second training session is performed in a carbohydrate-depleted state. Burke writes, “Despite increasing the muscles adaptive response and reducing the reliance on carbohydrate utilization during exercise, there is no clear evidence that these strategies enhance exercise performance.” In other words, even though these methods have the desired effect on the targeted mechanism, this effect does not produce the desired final outcome of increased performance.
This conclusion suggests that increasing fat-burning capacity is not as important as many endurance athletes, coaches, and experts believe it is. No one can deny that it’s very important, but it seems to be not so important that athletes should orient the entire training process around it.
My take on the matter is that we have another example of the common mistake of training physiology instead of training performance. This mistake always consists, in one way or another, of choosing some physiological adaptation, whether it’s increasing fat-burning capacity of increasing anaerobic threshold or something else, as the singular be-all and end-all of training. The problem with doing so is that the physiology of exercise is incredibly complex, such that no individual adaptation can be singled out as most important.
Looking “under the hood” at the physiological changes that underlie improvements in endurance performance can be interesting, but all too often it becomes a distraction from what really matters, which is improved performance—a classic example of missing the forest for the trees. The simplest and most reliable way to attain the goal of optimal race performance is to leave the hood down and focus on training for that goal. This entails paying attention to distance, time, and pace instead of things like heart rate, blood lactate level, and rate of respiratory exchange ration.
For example, if your goal is to run a three-hour marathon, your job is to build the endurance you need to run 26.2 miles and to become comfortable and efficient in running 6:52 miles. By relying on conventional, proven marathon training methods, your own trial and error, and a dash of common sense, you can do this job very effectively without knowing the first thing about how your training affects your physiology.
A well-designed and executed marathon training plan will increase an athlete’s fat-burning capacity significantly without including any out-of-the-way efforts aimed at this particular effect. But guess what? It will probably increase the athlete’s carbohydrate-burning capacity even more. And that’s a good thing, because the typical runner capable of running a three-hour marathon will get in the neighborhood of 75 percent of his or her muscle energy from carbohydrate during the race, no matter how much he or she has trained for increased fat-burning capacity. Our muscles simply cannot burn fat fast enough to make it a major energy contributor at faster speeds.
I’m not suggesting that there’s no place in training for carbohydrate-deprived training sessions. It’s good to challenge your body in a variety of ways in the training process, and this is one relevant way to add variety. Just be sure you don’t pack your training so full of such workouts that you crowd out other sources of variety on the basis of an inflated sense of the importance of fat burning.
Check out Matt’s latest book, RUN: The Mind-Body Method of Running by Feel.