Proteins are essential macronutrients made up of smaller molecules called amino acids. In total, there are 20 amino acids of which 8 are considered ‘essential’ (if histidine is included the number of essential amino acids is 9. Histidine is essential mainly in infants). The term essential, in this case, indicates that the amino acid cannot be made by the body under any conditions, because humans lack of the specific enzymes needed to synthesize them. Non-essential therefore, indicates those amino acids that are readily manufactured within the body.
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