Protein powder is a concentrated protein supplement, sold as a dry powder to be mixed with water or milk into a drink. The main types are whey protein, casein, and egg white from animal sources, and soy, pea, rice, or hemp from plant sources, each differing in amino acid profile, digestibility, and speed of absorption. It is marketed chiefly to athletes, bodybuilders, and older adults seeking extra protein for muscle maintenance, recovery, or weight management. Quality varies: reputable products state protein content per serving and carry third-party testing, while cheaper blends may be padded with fillers or contaminated with heavy metals. Whole foods remain the preferred protein source for most people, with powders serving as a convenient top-up rather than a dietary foundation.