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What are essential amino acids?

Essential amino acids are the amino acids that the body cannot synthesise itself in sufficient quantities for physiological needs. Therefore, essential amino acids must be consumed in the diet. The 9 essential amino acids include phenylalanine, valine, threonine, methionine, tryptophan, histidine, isoleucine, leucine, and lysine. Food sources containing all essential amino acids are mostly animal products such as meat, fish, poultry, eggs, and dairy products. 

How many essential amino acids are there?

There are 9 essential amino acids: phenylalanine, valine, threonine, methionine, tryptophan, histidine, isoleucine, leucine, and lysine. These are the amino acids that all individuals need to consume for successful protein metabolism. However, under certain physiological conditions there are an additional 5 amino acids that can become conditionally essential. These circumstances usually present in individuals with compromised organ function, such as premature infants and individuals with inborn errors of metabolism. The conditionally essential amino acids include tyrosine, cysteine, proline, arginine, and glutamine. 

What are the non-essential amino acids? 

When amino acids are non-essential, it means we do not need to consume them from food because our body can synthesize them if we consume adequate amounts of all 9 essential amino acids. 

The non-essential amino acids are glycine, alanine, serine, cysteine, aspartate, glutamate, asparagine, glutamine, arginine, tyrosine, and proline. 

In special circumstances, some of the non-essential amino acids such as tyrosine, cysteine, proline, arginine, and glutamine can become conditionally essential.  

What foods are the best sources of essential amino acids? 

Foods that contain all essential amino acids are also known as complete proteins. Sources of complete proteins are mostly animal products such as milk, yogurt, cheese, eggs, meats, fish, and poultry. An exception is gelatin, which is of animal origin but lacks the essential amino acid tryptophan. Sources of complete proteins that are of plant origin are soy protein, quinoa, and chia seeds. 

How can I get all essential amino acids as a vegetarian? 

Plant foods such as legumes, nuts, seeds, vegetables, and grains either contain too little of one or more essential amino acids. Vegetables, legumes, peas, and lentils are usually low in methionine whereas nuts and seeds are low in lysine and threonine. Grains are usually low in lysine, threonine, and tryptophan. 

Lacto-ovo vegetarians should have no problem consuming adequate amounts of all essential amino acids because they still consume milk and eggs. 

Vegetarians who eliminate all animal products (also known as vegans) need to be intentional about combining plant-based proteins together at meals. To ensure proper essential amino acid intake at meals, vegans should pair grains, nuts, and seeds with legumes. Vegans should regularly consume the few plant proteins that contain all essential aminos acids: soy protein, quinoa, and chia seeds.

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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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