Final answer:
The primary function of protein in the diet is to serve as a metabolic fuel source. Proteins are also the major structural component of cells, especially muscles, and play various roles in immune response, cellular repair, and blood cell formation.
Step-by-step explanation:
The primary function of protein in the diet is to serve as a metabolic fuel source. Proteins are not stored for later use, so excess proteins must be converted into glucose or triglycerides and used to supply energy or build energy reserves.
Proteins also play a crucial role in the human body as the major structural component of cells, especially muscles. They are also involved in various functions such as acting as enzymes, carriers, and hormones, as well as participating in immune response, cellular repair, and blood cell formation.
Overall, protein is essential for growth, maintenance, and regulation of body functions.