Non-essential amino acids are the amino acids the human body can synthesise internally and therefore does not need to obtain from food under normal conditions. The group includes alanine, asparagine, aspartic acid, glutamic acid, serine, and, in healthy adults, arginine, cysteine, glycine, glutamine, proline, and tyrosine, though several of these become conditionally essential during growth, illness, or metabolic stress. Synthesis runs through transamination and other pathways using nitrogen from dietary protein and carbon skeletons from carbohydrate metabolism. The contrast with the nine essential amino acids is fundamental to protein quality: a food protein is judged by its essential amino acid content, since the body can make the rest. Nutrition labelling and amino acid scoring therefore focus on the essential fraction, treating the non-essential contribution as automatically covered.