Fat Excretion: How Your Body Eliminates Excess Body Fat

The National Institute of Health states that there are 3,500 calories in a pound of fat. So creating a 3,500 caloric deficiency is required to lose that pound in a week. But where does the fat go?

Fat Overview

• According to Teens Health, fats (also known as lipids) are nutrients in food that your body uses as fuel and to build nerve tissue and hormones. When fats aren't used in these three ways, they are stored as excess for later use. If you burn more calories than you are eating, your body targets its special reserves -- fat cells -- and begins to burn them.

Fat Breakdown

• Mayo Clinic nutritionist Katherine Zeratsky, R.D., L.D., explains that fat cells are made up of triglycerides (glycerol and three fatty acid chains). When your body burns fat cells, these compounds are broken down and used for energy through catabolism, or the breakdown of complex molecules into simpler ones, which releases of energy. The remaining compounds are absorbed into your liver, kidneys, and muscle tissues and used as energy and building blocks.

Waste Excretion

• What is not used for energy remains in the form of carbon dioxide and water and is excreted as waste. The water is released as sweat or urine, and the carbon dioxide is exhaled through your lungs.