A protein shake is a beverage made by mixing protein powder with water, milk, or other liquids. It is often consumed by athletes, fitness enthusiasts, or individuals looking to increase their protein intake. Common sources of protein in these shakes include whey, casein, soy, and pea protein. Protein shakes can be convenient for post-workout recovery or as a meal replacement. They may also contain additional ingredients like fruits, vegetables, or supplements to enhance their nutritional value. Many people enjoy them for their taste and ease of preparation, making them a popular choice for busy lifestyles.