Which amino acids are classified as essential?

Essential amino acids are those that cannot be synthesized by the human body and therefore must be obtained through the diet. There are nine amino acids classified as essential: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Since the body cannot produce these amino acids on its own, it is crucial to consume them in sufficient quantities through food sources, particularly protein-rich foods such as meat, dairy, and certain plant-based sources.

The other choices revolve around misconceptions about amino acids. For example, amino acids that can be synthesized by the body are termed non-essential, not essential. This fundamental distinction clarifies why option B accurately describes the specific requirement for essential amino acids. Understanding the classification of amino acids based on their synthesis is important for grasping the nutritional needs of the body and the role of dietary proteins in supporting health and growth.