Which types of amino acids cannot be synthesized by the human body?

The types of amino acids that cannot be synthesized by the human body are essential amino acids. These are the amino acids that must be obtained through diet because the body lacks the necessary pathways to produce them. There are nine essential amino acids in total, which include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Understanding essential amino acids is crucial because they play vital roles in various physiological functions, including protein synthesis, tissue repair, and nutrient absorption. A deficiency in essential amino acids can lead to various health issues, reflecting the importance of consuming a well-balanced diet that includes sources of these amino acids, such as meat, dairy, eggs, and certain plant-based proteins.

In contrast, non-essential amino acids can be synthesized by the body, while conditional amino acids are usually synthesized but may become essential during times of illness or stress. This distinction highlights why essential amino acids are critical for maintaining overall health, as they cannot be acquired through internal biosynthesis.