Chapter 3: Exercise Metabolism
Nutrition, Performance, and Recovery
Amanda Shelton
Putting Value into the Diet
There are a variety of components of the average daily diet that contribute to an effective nutrition strategy for improving exercise performance including optimizing your macronutrient, micronutrient, and fluid intake and timing of consumption to help provide a more effective and individualized dietary intake pattern. But first I want to give a little brief introduction to our essential nutrients for those who have never taken a nutrition course before.
Macronutrients
Energy-yielding Macronutrients include the nutrients that many people have at least heard of before:
- Carbohydrates
- Proteins
- Lipids (fats)
Carbohydrates4
Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms. Include our simple sugars such as glucose and fructose and complex sugars such as starch, glycogen, and cellulose. The complex sugars are also called polysaccharides and are made of multiple monosaccharide molecules. Polysaccharides serve as energy storage (e.g., starch and glycogen) and as structural components (e.g., chitin in insects and cellulose in plants).
Our simple sugars can be digested and absorbed quickly to provide energy via ATP to the cells during higher intensity activity. While our complex carbohydrates require a bit more time for digestion and absorption and can provide the body with a longer, slower release of energy over time.
Protein4
Much of the body is made of protein, and these proteins take on a myriad of forms. They represent cell signaling receptors, signaling molecules, structural members, enzymes, intracellular trafficking components, extracellular matrix scaffolds, ion pumps, ion channels, oxygen and CO2 transporters (hemoglobin). That is not even the complete list! There is protein in bones (collagen), muscles, and tendons; the hemoglobin that transports oxygen; and enzymes that catalyze all biochemical reactions. Protein is also used for growth and repair. Amid all these necessary functions, proteins also hold the potential to serve as a metabolic fuel source. Proteins are not stored for later use, so excess proteins must be converted into glucose or triglycerides, and used to supply energy or build energy reserves. Although the body can synthesize proteins from amino acids, food is an important source of those amino acids, especially because humans cannot synthesize all of the 20 amino acids used to build proteins.
Lipids4
Fats (or triglycerides) within the body are ingested as food or synthesized by adipocytes or hepatocytes from carbohydrate precursors (Figure). Lipid metabolism entails the oxidation of fatty acids to either generate energy or synthesize new lipids from smaller constituent molecules. Lipid metabolism is associated with carbohydrate metabolism, as products of glucose (such as acetyl CoA) can be converted into lipids.
Dietary Strategies for Performance7
There are several strategies that have been used to help improve an athlete’s performance during different activities. The most effective use of these strategies will depend on the individual, the type(s) of activity they participate in (both exercise and physical activity), and their dietary consumption outside of activity specific needs.
Carbohydrate Loading
This is one of the most popular strategies for improving performance, one that you may have done before! Ever have a Team Pasta Feed? Night before the event Team Dinner? These are common tactics for how we can maximize our muscle glycogen stores prior to an activity or event.
Why do we do it? To maximize the glycogen stores in our muscles prior to endurance exercise lasting longer than 90 minutes.
What’s the benefit? Delay the onset of fatigue and improve performance.
When do we do it? Best practices for this is a bit more involved than just eating pasta the night before.
- For events lasting longer than 90 minutes: Ideally, we are consuming ~10-12 grams of carbohydrates per kg of body mass per day in the 36-48 hours prior to the activity/event.
- For events lasting 60-90 minutes: ~7-12 grams of carbohydrates per kg of body mass during the 24 hours leading up to the activity/event.
Case Study
Suzie Cue is running in her first half marathon this weekend. Suzie has been practicing her in race food and hydration strategy throughout her training but is trying to figure out what meals to have leading up to the event.
Since she expects the race to take more than 90 minutes she uses the recommendation listed above to determine her carbohydrate intake on Friday and Saturday before her Sunday race.
First, we need to convert lbs to kg:
- = (140 lbs)/ (2.2 lb/kg) = 63.6 kg
Then we need to figure out how many grams of carbohydrate per day Suzie should consume based on her body mass:
- = 10 g * 63.6 kg = 636 g/day
- = 12 g * 63.6 kg = 763 g/day
**For reference, in a typical 2000 kcal/day diet, we are typically looking at 225-325g of carbohydrates per day**
For Suzie, what might this look like in a regular days consumption?
Breakfast: 132 g of carbohydrates
- Maple and Brown Sugar Instant Oatmeal (2 packets) = 66 g
- Banana (medium) = 27 g
- Orange Juice (12 oz) = 39 g
Mid Morning Snack: 47 g of carbohydrates
- Apple (medium) = 25 g
- Gatorade (1 bottle) = 22 g
Lunch: 223 g of carbohydrates
- Steak Burrito = 116 g
- 1 20 oz bottle of lemon-lime soda = 64 g
- Tortilla Chips and Salsa = 43 g
Mid Afternoon Snack: 60 g of carbohydrates
- 1 cup of Skim Milk = 12 g
- Graham Crackers (4 full crackers) = 48 g
Dinner: 147 g of carbohydrates
- Spaghetti with Meatballs = 99 g
- Garlic Bread (2 slices) = 36 g
- 1 cup Skim Milk = 12 g
Dessert: 54 g of carbohydrates
- Vanilla Ice Cream (1 cup) = 31 g
- Caramel Sauce (2 Tbsp) = 23 g
Total Carbohydrates for the day: 663 g of carbohydrates
With Carbohydrate Loading it is important to note that it is not necessarily what we would consider a “well-balanced” diet since it is significantly more carbohydrates than what would be recommended in the typical dietary pattern based on body mass. This is not a pattern that should be maintained throughout training and should only be used in situations where the length of endurance activity will be extended and performance is the intent. In our example with Suzie above, during her training if she had a “long run” midway through her training cycle that was a 7.0 mile run that she expected to take ~65 minutes, she would not necessarily need to go through the same intensive carbohydrate loading as dictated above.
In addition to the day(s) leading up to the event, with endurance activities specifically, it is important that we look to “fill” those stores as much as possible in the hours leading up to the activity/event.
- For events lasting longer than 60 minutes: 1-4 grams of carbohydrates per kg of body mass in the 1-4 hours prior to the activity/event.
Mid-Event Carbohydrate Intake
Similarly as with Carbohydrate Loading, when we have longer duration endurance events (particularly those that last longer than 60 minutes) it is important that we begin to consider consumption of carbohydrates DURING the activity.
Benefits of carbohydrates during activity:
- Prevent hypoglycemia (low blood sugar)
- Maintains high level of carbohydrate oxidation for utilization of energy
- Improves performance of long-duration activity (especially multiple hours of activity)
| Exercise Duration | Example Exercise Type | Carbohydrate Intake Per Hour |
| 30-75 minutes | 5k or 10k race | Small amounts or carbohydrate rinse |
| 1-2 hours | Soccer Game (90 minutes long) | 30 g |
| 2-3 hours | Half to Full Marathon | 60 g |
| >2.5 hours | Half Ironman Triathlon, Ultra-races | 90 g |
“Train Low, Compete High” Method
Within this particular method, different strategies exist. This method is sometimes also referred to as “fasted training” where you are restricting carbohydrate or total into prior to participation in your training activities. This may occur by participating in your training session after an overnight fast or by having a several hour fast prior to participating in a second training session in the day. With this, you would follow a similar carbohydrate loading strategy identified above immediately preceding your competition.
*Intended/Speculated Benefits:
- Enhanced cell-signaling pathways
- Increased mitochondrial enzyme content and activity
- Enhanced lipid oxidation rates
- Improved exercise capacity
*Not supported through scientific literature, further research is needed.
Unfortunately, this strategy has no clear evidence in the scientific literature to support these benefit claims and further research is necessary to identify the optimal strategy for this particular method.
Heather Ketchum & Eric Bright, OU Human Physiology Textbook. OpenStax CNX. Jun 18, 2015. Download for free at: http://cnx.org/contents/e4f804ec-103f-4157-92e1-71eed7aa8584@1
Beck K, Thomson JS, Swift RJ, von Hurst PR. Role of nutrition in performance enhancement and postexercise recovery. Open Access J Sports Med. 2015;6:259-267 https://doi.org/10.2147/OAJSM.S33605