Can the type of food you eat "turn off" your aerobic system?

The definition of the aerobic system is the “combustion of carbohydrates and fats in the presence of oxygen”. The aerobic system is how we produce energy from fuel for endurance efforts, which is necessary for all runners, no matter the pace. If we continually fuel, this system can keep functioning.

The aerobic system can be fueled by carbohydrates and/or fat. It is possible to utilize protein; however, the body spares protein breakdown at all costs. We know that when both carbohydrates and fat are available, turning carbohydrates into energy is more efficient and carbs are utilized more during high intensity exercise. If carbohydrates are not present, fat will be utilized as the fuel source.

Fat is utilized more at low-moderate intensities, but in the absence of carbohydrates, your body will indeed utilize more fat for energy. However, we also know that when glycogen is depleted, our bodies start to break down protein – and as endurance athletes, we want to build and support lean muscle, not break it down. Also, we mentioned above that the process of turning carbohydrates into energy is more efficient than fat <you will be able to give your body energy faster with carbs as the fuel source>, and carbohydrates are important for contractile function in the muscle.

Absolutely not. If you have fuel to use <aka carbs, fat, protein> and you are working at a higher intensity <aka high aerobic activity>, your aerobic system will produce energy from said fuel, no matter where they came from. Your energy systems do not know the difference between fuel from oatmeal, pop tarts, graham crackers, gels, or a banana.

A balanced diet with adequate protein at all meals, healthy fats, and matching carb intake for your current activity level is the best way to fuel your aerobic system. In our daily lives, for the most part, meals and snacks can consist of complex carbohydrates <giving you carbohydrates, fiber, and other nutrients>, lean protein, healthy fat, and color.

Being more strategic before and during your exercise with quick fuel sources that are easy to digest will help you get the energy you need the fastest, without upsetting your GI tract. Easily digestible carb sources: bagel, English muffin, toast, grahams, banana, etc.