Everything you eat must be broken down into simpler substances for your body to use. The three basic forms of macronutrients are protein, fat and carbohydrates. Protein is broken down into amino acids. Fat is broken down into fatty acids. All the basic nutrients can be used for energy if necessary, but your body favors carbohydrates. If there isn't enough glucose available, you can get energy from fat and then, through a more complex process, from protein.
Carbohydrates
Most carbohydrates are broken down by your body into simple sugars. The natural sugars you eat, such as sucrose, fructose, galactose and lactose, are also converted into the simplest chemical form of sugar, which is glucose. Even in this simple state, glucose is a complex molecule. Glucose is stored in your liver and muscle tissues as glycogen. When more glucose is needed, the glycogen is converted back into glucose and carried by your blood to your cells.
Cell Membrane
Every cell in your body requires fuel to make energy. The cell membranes are selective, and do not allow all substances to enter. Action is needed by other substances to allow them to cross the cell membrane. With glucose, the hormone insulin triggers the cell transport system that gets the glucose into the cell and stimulates your cells to metabolize it. Insulin also regulates the system that regulates using glucose, fat or protein for energy.
How It Works
Glucose itself is the main energy nutrient for your body. Vitamins, minerals and trace elements all have a part in the metabolism of basic nutrients. In the cell, glucose becomes energy by the action of chemicals which further break down the glucose molecule into an energy substance called ATP, which can be stored in your cells. ATP is the form of energy that your cells can use.
Considerations
Some cells, such as red blood cells and brain cells, can't store ATP energy, so must use it as it is formed. Glucose is the only form of energy fuel these cells can use. Glycolysis, or transforming glucose to energy, can be done with or without oxygen. When muscle cells make ATP without oxygen, there is a byproduct called lactic acid. Buildup of this acid may be what makes your muscles sore after exercise, but according to "Nutrition in Clinical Practice," there is some controversy about this. When ATP is made without oxygen, much of it is wasted, so the glucose stores are quickly depleted.
Conclusion
Glucose is the primary nutrient for energy, not used directly in the form of glucose, but in the form of ATP or adenosine triphosphate. The co-enzyme ATP is used by all known life forms as the energy molecule. No single nutrient is responsible for the conversion of glucose or other nutrients into ATP. Both a healthy diet and exercise maximize the process of converting food into energy.
References
- "Nutrition in Clinical Practice: A Comprehensive, Evidence-Based Manual for the Practitioner"; Katz, David L., Friedman, Rachel S.C.; 2008
- "Handbook of Pathophysiology" 3rd Edition; Corwin, Elizabeth J.; 2008
- "ACC Atlas of Pathophysiology" Cheryl A. Bean APRN, BC, DSN, AOCN, ANP and collegues; 2006
- Estrella Mountain Community College: Transport In and Out of Cells
