How many essential amino acids cannot be synthesized by the body?

The correct answer is nine essential amino acids. These are amino acids that the human body cannot synthesize on its own and, therefore, must be obtained from dietary sources. The nine essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

The body requires a total of 20 amino acids to function properly, but it can produce 11 of these through various metabolic pathways. However, the remaining nine essential amino acids are vital for numerous physiological processes, including protein synthesis, enzyme function, and hormone regulation. These amino acids must be consumed through protein-rich foods, such as meat, dairy, eggs, and plant sources like legumes and nuts, to meet the body's needs.

Understanding the distinction between essential and non-essential amino acids is crucial for nutritional science, as it impacts dietary planning and health.