What Are Complete Proteins? - Definition & Food Examples

Instructor: John Koshuta
Proteins are the body's building blocks and without them life would not be possible. But not all proteins are created equal. Some proteins are considered complete, while others are incomplete and need to be combined in order to be utilized properly. Understanding complete proteins can help an individual improve their diet and overall health.


Every part of our body needs protein in order to function properly. We must consume protein in our diets in order to replace body proteins that are broken down during normal functioning. When consumed and digested, proteins are broken down into various organic compounds known as amino acids. These 20 amino acids are then rebuilt within the body to create various structures including cells, muscles, and organs. While protein deficiencies are rare, knowledge of complete proteins remains critically important.

What Are Complete Proteins?

A protein that provides all nine essential amino acids is considered complete. Essential amino acids cannot be made within the body and must be provided by the diet. Only protein sources that provide all essential amino acids are considered complete. The nine essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylanaline, threonine, tryptophan, and valine. In contrast, an incomplete protein is low in one or more essential amino acids and must be combined with other protein sources to be utilized properly.

Examples of Complete Proteins

Adults and children consuming foods from animal sources are consistently consuming complete proteins. The following foods provide essential amino acids:

  • Meat
  • Poultry
  • Fish
  • Milk
  • Cheese
  • Eggs

While rice, corn, and beans also provide protein, they are incomplete and must be combined in order to meet the body's needs. Fortunately, consuming various incomplete protein sources can also provide essential amino acids. Individuals with dietary restrictions such as vegetarians need to consider other protein sources in order to meet the body's needs. Individuals limiting themselves to a narrow range of incomplete proteins may experience deficiency symptoms such as hair loss or fatigue.

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