Which nutrient plays a critical role in building and repairing tissues?

Proteins are essential nutrients that play a fundamental role in building and repairing tissues within the body. They are made up of amino acids, which are the building blocks that contribute to the structure of various tissues, including muscles, skin, organs, and enzymes. When the body undergoes stress, such as exercise or injury, proteins are needed to help heal and regenerate those tissues, facilitating recovery and promoting overall health.

Carbohydrates serve mainly as a source of energy; while fats are important for energy storage and hormone production, they do not contribute directly to tissue building and repair in the same way proteins do. Minerals are vital for various bodily functions, including the formation of bones and teeth, but they do not have the same structural role as proteins. Thus, the critical function of proteins in the growth, repair, and maintenance of body tissues is what makes them the correct answer in this context.