Amino acids are the organic molecules from which all the body's proteins are assembled. Each has an amino group, a carboxyl group and a unique "side chain" that determines its properties. Joining by peptide bonds, amino acids line up into protein chains.
Of the roughly 20 proteinogenic amino acids, 9 are essential: the body cannot synthesize them in sufficient amounts, so they must come from food. One of these is methionine.
Essential and non-essential
The nine essential amino acids — histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine — must come from food. The rest the body can make itself. Foods that contain all the essential amino acids in sufficient amounts (meat, fish, eggs, dairy, soy) are called complete protein; many plant sources are low in one amino acid or another, so they are combined.
BCAAs and muscle synthesis
Three essential branched-chain amino acids (BCAAs) are leucine, isoleucine and valine. Leucine serves as the main "signal" for muscle-protein synthesis, triggering the mTOR pathway. With age, muscles respond worse to this signal, which contributes to sarcopenia — the loss of muscle mass. So adequate protein and physical activity are especially important in later life.
Not only for muscle
Amino acids are not only "building material". They give rise to neurotransmitters (for example, serotonin from tryptophan), hormones, components of nucleotides and many regulatory molecules. Methionine, through SAM, takes part in methylation. So a balanced amino-acid profile of the diet affects the whole metabolism, not just the muscles.
Calculate using this marker
Calculators where Amino acids is used directly:
Frequently asked questions
Do you need to take amino-acid supplements?
Usually no: with enough varied protein in the diet, all amino acids come from food. BCAA supplements make sense only in certain situations and do not replace complete protein.
What is complete protein?
It is protein containing all nine essential amino acids in sufficient amounts — meat, fish, eggs, dairy, soy. Plant sources usually complement each other in composition.