The nutrient essential for building muscle tissue is protein. Proteins are made up of amino acids, which serve as the building blocks of muscle fibers. Adequate protein intake is crucial for muscle repair, growth, and maintenance, particularly after physical exercise or resistance training. Foods rich in protein include meat, poultry, fish, eggs, dairy products, legumes, and nuts. For those looking to build muscle, combining protein with a balanced diet and proper exercise regimens can optimize muscle synthesis and recovery, making protein a vital component in fitness and overall health.