Metabolism is the word used to describe the chemical and physical processes in the body that provide energy for the maintenance of life.
Energy is neither created nor destroyed; rather, there is a transfer. You can think of your body as a bank, an efficient investment system. Many transactions are made each day.
Food is the initial investment you bring to your bank. It provides a continuous supply of energy for the body cells, but it is not used directly. Digestion breaks down the carbohydrates, fats, and proteins into the simple forms of glucose, fatty acids, and amino acids, and these are deposited into different “accounts” in your body “bank.” Some glucose is processed and used quickly for energy, like paying cash for a purchase. The remaining glucose becomes glycogen and is stored in the muscles and liver, part of your body’s bank.
This is similar to a checking account that you can get funds out of whenever you need them. Fatty acids are long-term investments, similar to a savings account. They are not meant to be “cashed in” immediately.
Protein provides amino acid building blocks for growth or repair of body tissues and to synthesize enzymes and hormones. It is used as an energy source only during periods of starvation at the expense of other needed functions. Your body bank thinks of using protein to prevent going bankrupt but at the expense of other important functions in the body.
When your body bank cashes in some of the saved glycogen or fatty acids, they release energy to form a compound that is abbreviated ATP. This is the “currency” that is used to buy your body’s activity. All biological work requires that ATP be broken down or spent. The body cashes in its savings and produces ATP either anaerobically or aerobically.
Aerobic production of ATP is for activities requiring sustained energy at a slower pace. Your body bank cashes in either glycogen or fatty acids over a long period of time, similar to cashing in a savings bond and spending it slowly. Because of the negative publicity excess body fat gets, it’s hard to realize that from your body’s point of view, fat is the gold standard for potential energy.
Carbohydrates provide four calories of energy per gram. It is stored in the body as glycogen in sufficient quantity for a 10-mile run or about 1200 calories. Fat, which provides 9 calories per gram, is stored in almost unlimited abundance. A woman who weighs 120 pounds with 25 percent of her weight stored as body fat has enough stored energy to run 1000 miles.
The comparison of your body to a bank is a very simple way to explain the complicated process of energy use, or metabolism. As it pertains to exercise, the anaerobic and aerobic energy systems are not mutually exclusive. They can work together or the body can alternate between them. The intensity of an exercise period dictates the fuel, whether mostly glycogen or fatty acids are used.
People who love to exercise for fun and fitness can appreciate how effective the metabolic systems operate to allow the enjoyment of activity. If you need to decrease your energy investment and lose some body fat, go on a spending spree!
