Proteins are called body building foods because they play a crucial role in the growth, development, and repair of body tissues. They are responsible for building and repairing muscles, bones, organs, and other tissues. Proteins also help in the production of enzymes, hormones, and antibodies, which are essential for the proper functioning of the body. Additionally, proteins provide energy, although their primary function is not energy production. Hence, proteins are commonly referred to as body building foods.