Protein is an essential macronutrient composed of amino acids. It serves many functions in the body including providing energy, maintaining muscle mass, regulating hormones, and keeping blood pH balanced. Common protein sources include meat, eggs, dairy, nuts and legumes. Protein supplements can help individuals meet higher protein needs, especially athletes and bodybuilders seeking to build muscle. Supplements come in various forms and taking protein at key times like after workouts can maximize muscle growth and recovery when part of a resistance training routine.