Essential amino acids are those which cannot be synthesized in our body, so they must be obtained through the diet as they are necessary for the synthesis of proteins. Two examples are threonine and phenylalanine.

Non-essential amino acids are those which are not required to be taken in diet because they can be synthesized by the body itself. These amino acids are also important for the to form the building blocks of proteins. Two examples are proline and cysteine.