What are they: Like vitamins and minerals, certain amino acids are believed to be vital to the maintenance of human life. Amino acids are often described as chemical components or substrates for protein synthesis. They are the main components of muscles and tissues (second only to water). Studies in the past few decades have shown that they also have other important roles, such as acting as regulators of metabolic pathways in gene expression and cell signal transduction. Although people have conducted a lot of research on amino acids, there are still controversies in people's diet, at which stage in their lives, and even which amino acids they think are still needed for normal biological functions. Common amino acids: essential: histidine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine. Non-essential: alanine, asparagine, arginine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine.