Knowing how the food you eat becomes energy can help you make better food and meal choices. The food you eat is generally from one of three categories: protein, fats or lipids and polysaccharides, also called complex carbohydrates. There are three primary biochemical steps in metabolizing or breaking down food into energy, beginning with the enzymatic breakdown known as digestion.
Digestion
Digestion breaks down these large polymeric molecules into their respective monomer subunits. For example, proteins are broken down into amino acids, lipids are broken down into fatty acids and glycerol and polysaccharides are broken down into sugars. This initial enzymatic breakdown of the food you eat results in smaller organic molecules ready for step two of metabolism, which takes place primarily inside your cells.
Glycolysis Breaks Down Glucose
The cytosol is the fluid inside the cell, excluding the small organ-like structures known as organelles. Once inside the cytosol, these small organic molecules begin a slow oxidation process known as glycolysis. Glycolysis, the initial oxidation step, converts glucose and other sugar molecules into pyruvate. Pyruvate then enters the cellular organelle known for energy production, the mitochondria, ready for the final oxidation step.
Producing ATP for Energy
The final metabolic step your body performs for its energy is the production of ATP. ATP, or adenosine triphosphate, is used by every cell in your body for energy. This final step in metabolism takes place entirely in the mitochondria inside your cells. Roughly 1 billion ATP molecules are present in every cell of your body at any given moment and are used up entirely every one to two minutes.
Energy Requirements
Even when you are at rest, your body needs energy for its most basic functions such as breathing, heartbeat, blood circulation, growth and repair of your cells, and regulation and release of hormones. The energy requirements for these basic functions are known as your basal metabolic rate, or BMR. According to the Mayo Clinic, "Energy needs for your body's basic functions stay fairly consistent and aren't easily changed. Your basal metabolic rate accounts for about 60 to 75 percent of the calories you burn every day."
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