Amino acids in food make up protein. When protein is digested it is once again broken down into specific amino acids, these are then selectively put together for different uses. These new proteins formed in the body are what make up most solid matter in the body: skin, eyes, heart, intestines, bones and, of course, muscle.
More about amino acids
There are 20+ Amino Acids, with 8-10 of them considered essential, meaning that they cannot be synthesized in our body. These include the three BCAAs (Branched Chain Amino Acids) - Leucine, Isoleucine and Valine - as well as Histidine, Lysine, Phenylalanine, Methionine and Threonine.
Some Amino Acids are more important than others when it comes to fitness and muscle building. The BCAAs are the three most important amino acids in the manufacture, maintenance and repair of muscle-tissue.
Lysine plays a role in revitalizing the body to combat fatigue and overtraining and it maintains a positive nitrogen balance, creating an anabolic environment within the body.