The correct answer is option 1: Protein. Protein is known as the body builder because it plays a crucial role in building and repairing tissues in our body, including muscles. When we exercise or engage in physical activities like weightlifting, our muscles undergo wear and tear. Protein helps in repairing these damaged muscle tissues, promoting their growth and strength. It also provides the necessary building blocks for muscle synthesis.

Option 2: Carbohydrates are an important source of energy for our body, but they do not have the same direct role in muscle building as protein.

Option 3: Vitamins are essential for various bodily functions but do not directly contribute to muscle building.

Option 4: Fats are also important for energy and hormone production but are not specifically known as body builders.