The principal function of glycine is that it is an important building block of proteins. It is an essential amino acid that is used every day to strengthen your body and allow it to work properly. This amino acid is essential for many different muscle, cognitive and metabolic functions. It helps break down and transport nutrients like glycogen and fat to be used by cells for energy, and in the process, it supports strong immune, digestive and nervous systems. Glycine is the second most widespread amino acid found in human enzymes and proteins, which is why it has roles in nearly every part of the body. It's one of the 20 amino acids used to make protein in the body, which builds the tissue that forms organs, joints and muscles.