What exactly is protein? Some experts say it’s best to think of protein as a combination of up to 20 individual nutrients called amino acids, which are the building blocks of proteins and play various key roles in human metabolism. The digestive system breaks down the proteins you consume into amino acids, but the body can also make (“synthesize”) all but nine of the amino acids it needs. These “essential” amino acids must come from food:
Adults can make arginine, but for the young this is also an essential amino acid.
A human body that weighs 170 pounds will include almost 27 pounds of protein, nearly 16%, with water making up about 70% of the rest. About half of the body’s protein is used to form skeletal muscles, but every cell and all bodily fluids except bile and urine contain protein.
Proteins transport molecules from one place in the body to another, break down toxins and perform countless other maintenance chores. Your body needs protein to form new cells and repair old ones. Amino acids form the precursors of many important enzymes, hormones and other molecules the body needs. Amino acids also help protect the body against bacteria and viruses.