Which of the following is NOT a primary function of protein in the body?

Protein plays several vital roles in the body, including muscle building, tissue repair, and immune function support.

Muscle building is one of the most recognized functions of protein, as it provides the necessary amino acids that contribute to the growth and maintenance of muscle tissue. Similarly, proteins are essential for tissue repair, as they are involved in the regeneration of damaged cells and tissues after an injury. Immune function is also significantly supported by proteins; antibodies, which are crucial for fighting infections, are composed of protein.

On the other hand, bone mineralization is primarily the responsibility of minerals like calcium and phosphorus, along with the presence of vitamin D. While protein does play a role in maintaining bone health and providing some structural component, it is not directly responsible for the mineralization process that strengthens bones. Therefore, bone mineralization is correctly identified as not a primary function of protein, distinguishing it from the other listed functions that clearly involve protein.