What nutrient provides 4 calories of energy per gram and is essential for tissue building in the body?

The nutrient that provides 4 calories of energy per gram and is essential for tissue building in the body is protein. Proteins play a vital role in numerous bodily functions, primarily due to their role in the structure and function of cells. They are made up of amino acids, which are the building blocks of tissues such as muscles, skin, and organs. Additionally, proteins are crucial for repairing tissues, producing enzymes and hormones, and supporting immune function.

Carbohydrates also provide 4 calories per gram, but they primarily serve as a quick energy source rather than focusing on tissue building. Fats provide 9 calories per gram and are important for energy storage and cellular functions, but they do not contribute to building tissues like proteins do. Vitamins, while essential for various biochemical processes in the body, do not provide energy directly and are not building blocks for tissue. Thus, protein is the correct answer due to its unique role in energy provision and its critical importance in tissue growth and repair.