Primarily, the body uses proteins in growth and development for they are building blocks of cells, tissues, and organs. Moreover, the body uses proteins for repairing worn-out cells, tissues, and organs and maintaining their integrity. As the body requires chemical messengers, it uses proteins in the production of hormones such as insulin, thyroid hormones, and gonadotropins. The body also uses proteins in the production of enzymes such as lactase and amylase, which are essential in the digestion of food in the gastrointestinal tract into simple molecules for the body to absorb. To protect the body against diseases, the body uses proteins in the formation of antibodies, which are immune cells that attack antigens and neutralize their antigenic properties. During starvation, the body uses proteins in the production of energy to compensate for the deficiency in energy. In this view, the body derives proteins from cells, tissues, and organs, and breaks them down into amino acids before oxidizing them to produce energy.
There are numerous sources of proteins that the body can obtain in the form of a diet. Plant-based proteins are forms of proteins that a body can obtain from plants. Beans, peas, lentils, nuts, flax, spirulina, chia, and sesame are examples of plant seeds that are rich in proteins. Dairy products such as milk, cream, cheese, yogurt, and butter are important sources of proteins. Meat products generated from mutton, beef, pork, poultry, and rabbit are also integral sources of proteins. Seafood also provides important sources of proteins for organisms, for instance, fishes, crabs, shrimps, clams, and oysters are rich in proteins. Therefore, humans have numerous sources of proteins ranging from plants to animals.