Fuels for Exercise

It is true the body utilizes your food differently when exercising then when at rest. The body uses carbohydrates, fat, and proteins to provide necessary energy to maintain cellular activities both at rest and during exercise. However, during exercise the primary nutrients used for energy are fats and carbohydrates. Protein contributes a small amount of the total energy used (one of the many reasons I don't support high protein diets, like Atkins).

Carbohydrates

Carbohydrates are composed of carbon, hydrogen and oxygen. The stored carbohydrates provide the body with rapid availability of energy. Every 1 gram of carbs yield 4 kcal of energy. Carbohydrates exist in three forms:

1. monosaccharides - glucose (referred to as blood sugar) and fructose
   
2. disaccharides - sucrose (ex. table sugar)
   
3. polysaccharides - starches (when ingested, broken down to form monosaccharides and used as energy, or stored to use as energy later)

Glycogen is the term used for polysaccharides stored in animal tissue. Glycogen is stored in both muscle fibers and the liver. Glycogenolysis is the process of using glycogen for energy during prolonged exercise.

Fats

Stored body fat is an ideal fuel for prolonged exercise beacuse fat molecules contain large quantities of energy per unit weight. One gram of fat contains 9 kcal of energy, more than twice the amount of carbs and protein!

Fats can be categorized into four groups:

1. Fatty acids
2. Triglycerides
3. Phospholipids
4. Steroids

Proteins

Proteins are composed of amino acids. There are at least 20 types of amino acids needed by the body. Nine amino acids, called "essential amino acids" cannot be synthesized by the body, and therefore must be consumed in foods. For every 1 gram of protein there are 4 kcal of energy. During exercise protein is the last fuel source to be used, which is why protein is not a good preworkout food. Proteins main function is to rebuild and repair tissues after exercise.


It is very important to understand the basics of carbohydrates, fats and proteins. This is going to be especially useful as I start posting more about how to target each source when your goal is endurance exercise, losing fat, building muscle and so forth.