Thrive: The Vegan Nutrition Guide to Optimal Performance in Sports and Life

ensure the body is provided with enough simple carbohydrate to fuel activity so that complex carbohydrate is not relied upon. If the body has to resort to burning complex carbohydrate while exercising at a high intensity, it will have to use extra energy to convert the complex carbohydrate into simple carbohydrate.
     
    Eating too much protein before intense exercise will likely result in muscle cramping, since protein requires more fluid to be metabolized than carbohydrate or fat, and cramping occurs when the body is not properly hydrated. Also, protein is not what you want to have your body burning as fuel. Protein is for building muscle, not fueling it. When protein is consumed in place of carbohydrate immediately before exercise, and therefore burned as fuel, it burns “dirty,” meaning that toxins are created from its combustion. The production and elimination of toxins are a stress on the body and cause a stress response, ultimately leading to a decline in endurance.
     

the pre-exercise snack
     
    The most important factor in a pre-exercise snack is digestibility. If the food eaten shortly before a training session, race, or even a routine workout requires a large amount of energy to digest, it will leave the body with less energy—the last thing you want before exercise. Food that is difficult to break down requires more blood to come to the stomach to aid in the digestion process. When blood is in the stomach, it can’t be elsewhere delivering oxygen and removing waste products, tasks that must be carried out in order for you to achieve optimal physical performance. And if food has not been digested completely before you begin exercising, you may get a stitch—a cramp in the diaphragm. The more intense the exercise, the more important the digestibility of the pre-exercise snack is.
     
    The ratio of carbohydrate, fat, and protein in the pre-exercise snack is determined by the intensity and duration of the activity. There are three basic levels:
     
     
    Level One: High intensity, shorter time; activity lasting one hour or less.
     
     
    Examples: A three- to six-mile run; intense gym workout; game of basketball, tennis, hockey, soccer, or other quick-moving sport that involves lots of intense movement and then rest.
     
     
    Level Two: Moderate intensity, moderate time; activity lasting between one and three hours.
     
    Examples: Half marathon, marathon, Olympic distance triathlon, intense cycling, power hiking; activities involving more sustained output but less intensity than level-one activity.
     
     
    Level Three: Lower intensity, longer time; activity lasting more than three hours.
     
     
    Examples: Half Ironman, Ironman, bike ride, hike, long walk, adventure racing, days spent on your feet in everyday activity.
     
    The intensity of the activity will determine the fuel mixture burned by the body, as illustrated below:
     
    Sources of Fuel During Exercise
     

     

     
    Source: L. Bravo. Polyphenols: Chemistry, dietary sources, metabolism, and nutritional significance. Nutr Rev 1998, 56(2):317-33; M. Colgan. Optimum Sports Nutrition. New York: Advanced Research Press, 1993.
     
    The graph on page 110 shows what source of fuel the body is using when performing various intensities of exercise. Of course, everyone’s fuel requirements are slightly different, depending on fitness level, diet quality, and, to a lesser degree, genetic makeup. For longer exercise sessions and races, the fitter and better trained the body, the greater percentage of fat is utilized as fuel—preserving carbohydrate stores and in turn increasing endurance.
     
     
    Level-One Activity. For short bouts of high-intensity exercise, fuel up on simple carbohydrate. The healthiest source is fruit. Dates are a good choice since they are rich in glucose, a simple carbohydrate. Glucose, once consumed, goes straight to the liver for immediate energy; the body does not have to convert it to a different form in order to utilize it. This makes glucose-rich foods the best primary fuel before or during a high-intensity workout. However, it burns quickly, which means that if glucose is the only carbohydrate source, it will need to be replenished about every 20 minutes after one hour of intense activity to keep the body adequately fueled.
     
    Fructose, also a fruit sugar, has a lower glycemic index than glucose, meaning it kicks in at a slower rate once consumed, and it burns more slowly, which prolongs its effectiveness. Agave nectar,