Essay About Main Classes Of Food And Human Body

Proteins
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PROTEINS.
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 food. Foods high in protein include cheese, eggs, fish, and milk. All proteins contain carbon, hydrogen, nitrogen, and oxygen. Some proteins also contain iron, phosphorus, and suffur. Proteins are large complex molecules made up of smaller units called amino acids. Proteins make up a large part of each cell in the human body. Therefore, they are important in building, maintaining, and repairing tissues in the human body, especially bone cartilage and muscle. The body obtains most of its energy from carbohydrats and fats. However the body uses proteins for energy when carbohydrates and fats cannot meet its energy needs. Proteins produce about 1,800 calories of energy per pound (4 calories per gram0, the same amount provided by carbohydrates. 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.