What is Fatty Acid Oxidation? - Regulation, Steps & Mechanism

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Fats are a high energy source for the body. This energy is obtained through fatty acid oxidation. We will learn the steps of fatty acid oxidation and how it is regulated.

Energy from Fatty Acids

When you eat fried food, you are consuming a lot of fat. The body is able to gain a lot of energy from a single molecule of fat. For comparison, each gram of fat (on average) gives the body 9 calories of energy while a gram of protein or carbohydrates only gives 4 calories of energy.

Or, to look at this in another way, 1 molecule of glucose will give the body 30-32 molecules of ATP (energy). While 1 molecule of palmitic acid (a 16 carbon fatty acid) will produce 160 molecules of ATP!

The exact number of ATP produced from a molecule of fatty acid depends on the type of fatty acid. Longer chain molecules will produce more ATP. The process of creating energy from fatty acids is called fatty acid oxidation, or beta oxidation.

Beta Oxidation Steps

Beta oxidation of fatty acids includes four basic steps that are repeated over and over again until the entire molecule has been oxidized. Each of these basic steps creates an acetyl-CoA molecule, which is used in the citric acid cycle to create:

  • 2 ATP molecules
  • 6 NADH molecules (each of which forms 2.5 molecules of ATP)
  • 2 FADH2 (each of which forms 1.5 molecules of ATP).

Let's go over the four basic steps.

1. Acyl-CoA dehydrogenase creates a double bond between the alpha and beta carbons on the fatty acid. The hydrogens are added to FAD creating a molecule of FADH2.


A hydrogen is removed from the alpha and beta carbon atoms. Following the pink box, it will become the acetyl CoA
Step 1


2. Enoyl-CoA hydratase adds a water to the double bond, putting an OH onto the beta carbon and a hydrogen onto the alpha carbon.


Water is added to the molecule, the pink box represents what will become acetyl CoA
Step 2


3.Beta-hydroxyacyl-CoA dehydrogenase makes the carbon-OH bond a double bond between the carbon and oxygen. The lost hydrogen is added to NAD+ forming NADH.


The hydrogen atoms are removed forming a carbon oxygen double bond. The pink box represents what will become acetyl CoA
Step 3


4. Acyl-CoA acetyltransferase cuts off the first two carbon atoms, forming an acetyl-CoA and a new fatty acid that is 2 carbons shorter than the previous fatty acid.


The acetyl CoA is removed from the fatty acid, forming a shorter fatty acid
Step 4


This process repeats until all of the carbon atoms have been cut off. So, a 16 carbon fatty acid will repeat this process seven times, creating 8 acetyl-CoA molecules.

Fatty Acid Oxidation Regulation

The body tightly regulates how much energy is created based upon the energy needs of the body. If the body doesn't need more energy, the fatty acids won't be used to create energy. Instead they will be put into storage for later use.

One of the products in the citric acid cycle is malonyl-CoA. When malonyl-CoA builds up in the body this turns off beta oxidation and turns on fatty acid synthesis.

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