Metabolism: Definition & Overview

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  • 0:03 Metabolism
  • 0:48 Catabolism
  • 1:41 Anabolism
  • 2:36 Metabolism of Non-Foods
  • 3:14 Factors Affecting Metabolism
  • 3:54 Lesson Summary
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Lesson Transcript
Instructor: John Williams
Metabolism is the sum of all chemical reactions within the body. This concept, however, is much more complex than most of us understand. This lesson describes metabolism and the processes involved.


Have you ever known someone who can eat tons of food but never gains any weight? Or, how about someone who tries to lose weight, yet cannot seem to drop the pounds? We often blame metabolism for these two phenomena. Yet the concept of metabolism is one that is often poorly understood.

Metabolism is defined as the sum of all of the chemical reactions within the human body. This includes any chemical process by which a substance is broken down, produced, or chemically modified. Metabolism is often described in terms of food and nutrient use within the body, primarily because it is simpler to understand. In this lesson, we'll address the basic aspects of metabolism as it relates to food.


Imagine that you are eating a slice of pepperoni pizza. In that slice, you have several key nutrients that are necessary for life. You have proteins, which contain amino acids. You have starches, which contain sugars for energy. You also have fats, which can be used to produce energy and hormones. But, in order to get to the components that you need (like amino acids and sugars), you have to have a way to break down these materials.

Catabolism is the process of breaking down materials within the body. When we digest food, we are breaking down (or catabolizing) proteins, fats, and starches in order to get the useful components. This is done by adding water to the chemical bonds within these substances, which is a process known as hydrolysis. Foods that are indigestible, or cannot be broken down, are not able to be hydrolyzed within the body.


In order for our bodies to function, we must be able to produce materials that we need from the ones we digest. After catabolizing our food, we are left with the fundamental components that we need for life. For example, if we have tissues that are damaged, we have to produce proteins to heal those tissues. Therefore, the amino acids we receive from our food can be used to rebuild proteins. Sugars produced by digesting starches can be used to produce larger sugars for storage. Fats can be reproduced to store energy. All of these materials are made through anabolism.

Anabolism is the process of making larger substances from smaller materials. It is, in a sense, the opposite of catabolism in that it is achieved by removing water to create bonds. This process is known as dehydration synthesis. Through dehydration synthesis, we are able to make proteins, fats, and other needed materials.

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