Catabolism: Definition & Examples

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  • 0:04 What Is Catabolism?
  • 1:41 Digestion
  • 2:34 Glycolysis
  • 3:03 Beta Oxidation
  • 4:38 Lesson Summary
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Lesson Transcript
Instructor: Laura Foist

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

In this lesson, we will learn about catabolic reactions and how they create energy for the body. Learn more about catabolic reactions and why they're important to the body before testing your knowledge with a quiz.

What Is Catabolism?

A hamburger is not only delicious, but it may also give you energy to go about your day's activities. But how does that hamburger turn into energy? It happens through several reactions, all of which are catabolic. Catabolism is the breakdown of molecules into simpler ones. This process releases energy that can be used to fuel growth and activities, such as running or jumping.

Let's return to that hamburger from earlier: It contains fat, protein, and carbohydrates. These are all basic sources of energy on which our bodies rely. The body can either immediately break them down for energy, or it can store them for later use: protein in the form of muscle, fat in the form of body fat, and carbohydrates in the form of glycogen, which is a starch-like structure. For the body to use these substances for energy, they need to be broken down into smaller pieces through the process of catabolism. After being broken down into their simplest possible forms, energy can be released for use by the body.

The opposite of catabolism is anabolism, the process of using simple molecules to create more complex units. This is how muscle, bone, and other parts of the body grow and are maintained. However, the two are interrelated, since catabolism must break down the molecules that anabolism then uses to create more complex units.

The body has many catabolic reactions that take place to provide the body with usable energy. Lets look at the main ones that occur when you eat a hamburger in order to extract and utilize all of its energy: digestion, glycolysis, and beta oxidation.


In order for us to eat the hamburger, we first chew it up. This is similar to the catabolic process. The teeth don't actually cause a reaction to occur, but a larger material is being broken down into smaller ones. Later in the process, enzymes in the saliva, stomach, and intestines actually break the larger molecules down into smaller ones:

  • Protein gets broken down into individual amino acids.
  • Carbohydrates get broken down into monosaccharides or disaccharides, such as maltose or glucose.
  • Fat triglycerides get broken down into individual fatty acids.

Once the body has started the digestion process, these simpler units can be absorbed into the body. The energy from digestion cannot be stored by the body; rather, during the digestion step, the purpose is to create small enough molecules for the body to absorb.

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