How many amino acids are considered essential for human health?

The correct number of essential amino acids for human health is nine. These essential amino acids cannot be synthesized by the body and must be obtained through diet. The confusion often arises because some sources may mention 20 amino acids in total as there are 11 non-essential amino acids that the body can produce.

While 21, 22, and 23 could potentially refer to additional modifications or unique amino acids used in specific biological contexts, in the standard context of human nutrition and health, the focus rests on the nine essential amino acids that must come from food sources. Thus, the correct answer reflects a misunderstanding of amino acid classification in human health.