Chemical substances called hormones, many of which are proteins, control such processes as growth, development, and reproduction. The body obtains most of its energy from carbohydrates and fats. However, the body uses proteins for energy when carbohydrates and fats cannot meet its energy needs. Enzymes in the stomach and in the intestines break down the coagulated proteins into individual amino acids. The amino acids are absorbed into the blood and travel throughout the body.
Every cell assembles the amino acids into the proteins it needs.
For a detailed description of how a cell produces proteins, see Cell . Food containing proteins should be included in the daily diet because the body cannot store proteins for later use. The body converts excess proteins into carbohydrates and fats. If the body does not receive enough proteins from the food eaten, it uses proteins from the cells of liver and muscle tissues. However, continued use of such proteins by the body can permanently damage those tissues.