Which macronutrient is primarily responsible for building and repairing tissues?

Protein is the macronutrient primarily responsible for building and repairing tissues. This is due to its role in cellular structure and function. Proteins are composed of amino acids, which are the building blocks necessary for the synthesis of new tissues, including muscles, skin, organs, and blood. Additionally, proteins are involved in the production of enzymes and hormones that regulate many bodily functions, further contributing to tissue repair and overall metabolic processes.

Carbohydrates mainly serve as a source of energy for the body, while fat plays a key role in energy storage, insulation, and hormone production, but does not directly contribute to tissue building. Water, while essential for hydration and various physiological processes, is not a macronutrient that provides building blocks for tissues. Thus, protein's specific functions in growth and maintenance distinctly highlight its importance as the macronutrient responsible for tissue repair and construction.