What nutrient is composed of amino acids and is essential for building body tissues?

The nutrient essential for building body tissues is protein. Proteins are made up of long chains of amino acids, which are the building blocks that help repair and grow tissues, including muscles, organs, skin, and hair. In addition to their structural role, proteins are crucial for the production of enzymes and hormones, which play key roles in various bodily functions.

While carbohydrates and fats serve as energy sources for the body, they do not have the same functional significance in tissue building as proteins do. Carbohydrates primarily provide energy and are stored as glycogen, while fats serve as concentrated energy reserves and contribute to cell membrane structure and hormone production. Vitamins, while essential for various biochemical reactions and overall health, do not contribute to the structural framework of body tissues in the way that proteins do. Thus, protein is the correct answer as it directly relates to tissue synthesis and repair.