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What are complementary proteins? 

Complementary proteins are proteins from different foods that when combined supply the body with all 9 essential amino acids. 

Why do I need to complement proteins? 

Whereas animal sources of protein have all 9 essential amino acids, plant-based proteins typically are limiting in one or more essential amino acids. The body needs all 9 essential amino acids to synthesize protein in the body. 

The 9 essential amino acids are phenylalanine, valine, threonine, methionine, tryptophan, histidine, isoleucine, leucine, and lysine. 

Plant-based proteins are usually limited in methionine and/or lysine. If an individual consumes animal products along with plant-based proteins, it is unlikely that person needs to be concerned about complementing proteins. However, a vegetarian that does not consume any animal proteins (also known as a vegan), needs to be very conscious about complementing proteins to get adequate amounts of all 9 essential amino acids for proper protein synthesis. 

What are examples of complementary proteins? 

There are a few plant-based proteins that are complete, meaning they have all 9 essential amino acids: soy protein, quinoa, and chia seeds. However, most other plant-based proteins have one or more limiting essential amino acid. 

Wheat, rice, corn, and other grains are limiting in lysine, threonine, and tryptophan. 

Vegetables, legumes, peas, and lentils are limiting in methionine. 

Nuts and seeds are limiting in lysine and threonine. 

To ensure the body receives all 9 essential amino acids, pair plant-based proteins according to amino acid content. In general, pair vegetables, legumes, peas, and lentils with grains, nuts, and seeds. Examples of complementary proteins are green beans and almonds; rice and beans; corn tortillas and beans; vegetables and hummus. 

How much protein do I need a day if I consume a plant-based diet?  

If you are consuming solely plant-based proteins, you may need more protein than the average adult. This is because plant-based protein has a lower digestibility than animal based proteins. The recommended dietary allowance (RDA) of protein per kg of body weight in adults is 0.8 grams/kg per day. However, healthy vegetarians and vegans may require closer to 1 gram of protein per kg of body weight per day to meet protein needs. This protein should be spread throughout the day and each meal should contain complementary proteins to provide adequate amounts of all 9 essential amino acids. 

Related Terms

Metabolites

Learn more about Complementary Proteins:

Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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