Protein is an important nutrient to the human diet, supplying the body's needs for nitrogen and amino acids, those building blocks of proteins. The exact amount of dietary protein needed to satisfy these requirements might vary widely depending on age, sex, level of physical activity, and medical condition.

For instance, when we exercise hard, our muscles get micro tears in them. Our body then repairs these small tears in part with the amino acids provided by protein. If there are enough amino acids available, the muscle will also grow bigger and stronger to better handle the next time we stress it with work.