Complete protein sources contain all nine essential amino acids that the human body cannot produce on its own and must obtain from food. Incomplete protein sources lack one or more of these essential amino acids or have them in insufficient amounts.

Complete Proteins

• Contain all nine essential amino acids in adequate amounts.
• Typically found in animal-based foods such as meat, fish, poultry, eggs, and dairy products.
• Some plant-based foods are also complete proteins, including soy, quinoa, seitan, and buckwheat.

Incomplete Proteins

• Missing one or more essential amino acids or have them in too low quantities.
• Mostly found in plant-based foods such as nuts, seeds, beans, legumes, whole grains, and vegetables.
• Incomplete proteins can be combined with other protein sources over the course of a day (complementary proteins) to provide all the essential amino acids the body needs.

Key Notes

• The terms "complete" and "incomplete" can be misleading because even incomplete proteins contain all essential amino acids, but not always in amounts sufficient for the body's needs.
• A varied diet with a mixture of protein sources can ensure adequate intake of all essential amino acids.
• Complementary protein pairings like rice and beans, peanut butter and bread, or hummus and pita can form complete proteins when eaten together.

Thus, the main difference lies in the presence and adequacy of all nine essential amino acids in the protein sources.