Exercise-Specific Nutrition Needs
Good nutrition and proper hydration are important, but for regular exercisers or athletes, it can mean the difference between poor workouts and performance and outstanding performance. All macronutrients (carbohydrates, protein, and fat) are converted into ATP or useable energy. However, how this happens will depend on the type and intensity of exercise you do and will determine the fuel that is most appropriate for you.
ATP must be continuously generated during exercise since it is not stored in your body. Nutrients in your body are converted to ATP via four different energy systems. Which nutrients are used depends on the length and intensity of the activity.
1. Phosphagen – this system is used during the first few seconds of maximal effort (i.e. volleyball spike, tennis serve, 50-100 meter sprint).
2. Anaerobic Glycolysis – after the first few seconds of maximal effort, ATP is converted solely from carbohydrates. This energy system is used during activities that are high intensity and short duration (i.e. sprints, weight lifting sets). You will usually reach fatigue based on a build-up of lactic acid which causes physical pain in the muscles making it difficult to continue.
3. Aerobic Glycolysis – requires oxygen to convert nutrients to ATP and can use carbohydrates, proteins or fats).
4. Fatty Acid Oxidation – this energy system is involved for long-distance endurance activities typically lasting longer than 90 minutes. At this point, your body no longer has any carbohydrate stores and must convert fatty acids to ATP in order to continue.
If you plan to workout at moderate-to-high intensity levels, you need carbohydrates. At higher intensity levels, glucose (derived from carbohydrates) is what your body uses for fuel; your carbohydrate metabolism is more efficient than your fat metabolism at this level. Whether your activity is weight lifting or anaerobic sprints or intervals, you need carbohydrates.
If you are competing in an event lasting longer than one hour or continuing a high-intensity workout, you will likely need to replenish your carbohydrate stores. It is a common misconception that “running out” of carbohydrate stores will force the body to burn fat. Your performance will decline (some people may even be stopped by “hitting a wall”) because your body cannot maintain a higher intensity without having carbohydrates to convert to ATP. Some well-trained individuals can go as long as 2 hours before they need to replenish their body’s carbohydrate stores, but this also depends on how well they have replenished their stores in the days leading up to the event.
If you plan to workout for long periods of time at a low intensity, fat can serve as your body’s fuel source. In fact, at lower intensity levels, fat metabolism is more effective than carbohydrate metabolism and can continue being converted to ATP for several days (assuming your body lasts that long).
Where Does Protein Fit In?
Protein functions to build new and repair damaged proteins in your body; it is not primarily used as a fuel source during exercise. However, as you incorporate more intense workouts into your exercise routine, you may need slightly more protein in order to allow your body to repair from the stress of the workouts.
Do I Need to “Carb-Load”?
It’s a common misconception that eating a huge pasta dinner the night before a big event will help your performance. Unless your event is lasting longer than 1-2 hours, carb-loading is probably not necessary. However, maximizing your body’s glycogen stores (stored form of carbohydrate) in the days and weeks leading up to the event can impact your performance. Ideally, you want to begin an event with the maximum amount of glycogen stores. After each workout (particularly after strenuous workouts), you should be replenishing those stores by eating high quality carbohydrates. This is the best way to ensure your glycogen stores are maximized. When you taper your training and rest in the days leading up to longer events, you should be eating high quality carbohydrates. If you haven’t done this, then “loading up” the night before won’t do you much good.