After you eat a meal, your body stores part of the fat content from what you have consumed as fat in your body. These fats, called triglycerides, become the body's reserve in which it can produce energy to live, work and survive. When you exercise, or do any type of work throughout the day that requires energy, your body enacts a series of metabolic processes that use this storage of fat to create energy to do the work needed.
Fats have the highest potential for energy. The potential for energy can be calculated by examining how many calories are in a block of nutrition. The three main sources of energy are fats, carbohydrates, and protein. Carbohydrates and proteins both contain only four calories per gram; However, fats contain nine calories per gram, or approximately 3,600 calories of energy per pound. When you exercise to lose weight, fat is usually the first area in which the body chooses to create energy from, which, in turn, causes you to lose weight.
When you consume fewer calories than your body needs, the body automatically starts using its stored fat reserves to keep creating the necessary energy needed to operate. To do this, the body breaks down triglycerides into to two different substances, fatty acids and glycerol. These two substances are then transported to the muscles, liver, and kidney where they are absorbed and turned into energy to fuel the body.
At this point much of the original fat has been expended and burned off as energy; However, the metabolic processes that created the energy, also create waste products. This is how the remaining fat is released from the body. The creation of energy creates two main byproducts, carbon dioxide and water. The carbon dioxide is released from the body through the lungs when you exhale. The water created from the fat burning process is released through either sweat or through urine.