Essential amino acids are the nine types of amino acids that the body cannot produce and must obtain through diet. They matter because they play vital roles in protein synthesis, hormone production, and neurotransmission. These amino acids are crucial for growth, recovery, and maintaining overall health. Foods rich in essential amino acids include meat, fish, dairy products, and certain plant-based sources, such as quinoa and soy. Adequate intake is vital for optimal health and well-being.