Non-essential, in nutrition, describes a nutrient the body can manufacture for itself in sufficient quantities, so it is not strictly required in the diet. The classic examples are the non-essential amino acids, which the body synthesises from other amino acids and metabolic intermediates, and compounds like cholesterol, which the liver produces. The label is conditional rather than absolute: under stress, rapid growth, illness, or prematurity, synthesis may fall short and some non-essential nutrients become “conditionally essential,” as with arginine in severe injury or cysteine in premature infants. The distinction guides dietary recommendations, which set requirements only for nutrients the body cannot make, and it shapes protein quality assessment, where the essential amino acid profile is what limits a protein’s nutritional value.