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• Evaluating a Collegiate Athlete’s Diet
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• Myths About Sport Nutrition
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Myth 4

I'll burn more fat if I don't eat before I work out in the morning.

Sally Hara, RD, MS, CDE, responds:

This is one of those beliefs that is half a bubble off from the truth. In reality, we are always burning a combination of carbohydrate, fat, and protein when we exercise. It is the ratio of each that shifts according to many variables, including exercise intensity and duration, state of conditioning, and dietary intake, to name a few.

Our bodies tend to burn what's available. If we eat a high-fat meal, we have more fat in our system, and thus burn more fat. However, this does not imply that we burn more body fat. We simply use the type of fuel that was supplied. Likewise, if we consume greater amounts of carbohydrate, carbohydrate provides more fuel during exercise. Our bodies store a limited amount of carbohydrate in the form of glycogen, but after an overnight fast, glycogen stores are about 80% depleted because they are used to keep our blood-sugar levels stable while we sleep. That said, the other primary source of stored energy is fat. So if we don't eat anything before working out, we have more fat than carbohydrate available to use as a fuel during exercise. This is where some people get the idea that more fat is burned if they don't eat before exercising. But that's not the entire story.

It is important to realize that not all of the body fat burned as a result of exercise is burned during exercise. In fact, when we exercise we create a calorie (energy) deficit. The fuel used to create this deficit (fat or carbohydrate) is not likely to be important. What is important is what happens during the recovery time after exercise when the body makes up for this energy deficit, largely by pulling fat out of storage. Therefore, the bigger the deficit one can create during exercise, the greater the fat burned as a result of exercise. Research has demonstrated repeatedly that carbohydrate is the preferred fuel for exercise, allowing athletes to work longer and more intensely than when using fat as the primary fuel source. Therefore, eating breakfast provides enough fuel for a productive workout that allows you to create a bigger energy deficit. If you enhance your workout, you will increase the amount of fat you can burn in your postworkout recovery.

How did the expert counter this myth? Let's analyze the expert's explanation.