Proteins in the diet. How the body uses proteins. Protein Protein is one of the three main classes of food that provide energy to the body. The others are carbohydrates and fats. Proteins exist in every cell and are essential to plant and animal life.
Plants build proteins from materials in the air and the soil.
Human beings and animals obtain proteins from foods. Foods high in protein include cheese, eggs, fish, meat, and milk. The structure of proteins. All proteins contain carbon, hydrogen, nitrogen, and oxygen. Some proteins also contain iron, phosphorus, and sulfur.