A protein shake is a drink made by mixing protein powder with water, milk, or a milk alternative, sometimes with added fruit, oats, or flavourings. It is used mainly by athletes and gym-goers as a convenient way to raise protein intake around training, supporting muscle repair and growth, and by dieters seeking a filling low-preparation meal replacement. Ready-to-drink bottled versions are widely sold, though they cost more per gram of protein and often carry added sugars. Nutritionally a shake is only as good as its powder: whey and soy deliver complete amino acid profiles, while single plant sources may need blending. Shakes suit people with high requirements or poor appetites, but for most eaters a balanced diet already supplies enough protein without them.