An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. The nine essential amino acids — histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine — cannot be synthesised by the body and must be obtained from food. There are nine essential amino acids, which you must get through your diet — histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Although variations are possible depending on the metabolic state of an individual, the general held thought is that there are nine essential amino acids, including phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, leucine, and lysine. Nine amino acids—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—known as the essential amino acids, must come from food. A guide to the nine essential amino acids and their functions. The guide also examines the daily requirements and the best food sources. Amino acids are the building blocks of protein. Your body needs 20 amino acids to function correctly. Nine of these amino acids are called essential amino acids. Amino acids are the basic building blocks of proteins and help our bodies grow. Out of the 21 amino acids, only 9 are categorized as essential. Learn the amino acids our bodies need to function. There are 9 essential amino acids that your body needs to function and thrive but can't produce on its own so you need to get them from food. These are naturally present in the right amounts in animal proteins, though eating a variety of plant proteins can help you get enough of them too. Complete proteins contain all nine essential amino acids in proportions sufficient to meet the body's needs. Animal sources — meat, poultry, fish, seafood, eggs, and dairy — are reliably complete.