Which type of amino acids must be obtained from the diet?

Essential amino acids are those that cannot be synthesized by the body and therefore must be obtained through dietary sources. There are nine amino acids classified as essential for adults, which include leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and histidine. These amino acids play crucial roles in protein synthesis, tissue repair, and various metabolic processes.

In contrast, non-essential amino acids can be produced by the body, meaning they do not need to be consumed through the diet. Conditional amino acids may become essential under certain physiological conditions or stress but are generally not required in the diet under normal circumstances. Substitutable amino acids is not a widely recognized classification in nutrition, and therefore does not pertain to the need for dietary intake of amino acids.

Understanding the distinction between essential and non-essential amino acids is vital for nutritional science, as it underscores the importance of a balanced diet to meet the body's needs for amino acids that support overall health and function.