How the Body Burns Fat


For the most part, we view fat as the enemy. Yet, it’s important to recognize the fact that fat, like carbohydrates and proteins, can be converted into energy. Before you can fully understand the process, however, it is important that you know how food is converted into energy.

ATP is an acronym for Adenosine Triphosphate. It’s what the body uses as fuel at the cellular level. It can be produced with oxygen, aerobically, or without oxygen, or anaerobically. Meanwhile, glycolysis is an anaerobic process where glucose is converted into pyruvic acid. If oxygen is available, it is converted into acetyl CoA. However, if no oxygen is available, it is converted into lactic acid. The Krebs Cycle refers to an eight-step cycle which removes hydrogen and carbon-dioxide and produces a small amount of ATP. Lastly, the Electron Transport Chain refers to the final process in the breakdown of foods, where most of the ATP is formed.

The Breakdown of Fats

You should be aware of the fact that there are many fats in the body. However, it’s the neutral fats, or triglycerides, that are usually converted into energy. These fats come from both stored fat within fat cells and skeletal muscle fibers and from diet. In order to be used for energy, these fats need to be broken down into basic units. These units consist of one molecule of glycerol and three molecules of fatty acids, a process known as lipolysis. The glycerol and fatty acids must then be converted into acetyl CoA. Glycerol is converted into pyruvic acid, which is then converted into acetyl CoA.

This is accomplished in three steps:

  • One carbon is removed from the pyruvic acid and released as carbon dioxide, which exits the body through the lungs.
  • Hydrogen atoms are removed and will later produce more energy.
  • The remainder is known as acetic acid, which is combined with coenzyme A to produce Acetyl CoA.

Through beta-oxidation, fatty acids are converted into Acetyl CoA. The fatty acid chains are broken apart, forming two acetic acid molecules. These are then fused to coenzyme A, creating acetyl CoA. The glycerol and fatty acids are now prepared for the Krebs Cycle. When the acetyl CoA is broken down, carbon-dioxide and hydrogen are removed. The carbon dioxide exits the body through the lungs and the hydrogen moves to the final stage.

The final process in the break down of food is the Electron Transport Chain. The hydrogen molecules combine with oxygen to form water, or H2O. The energy that results from this reaction leads to the formation of ATP.


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