A protein source refers to any food or substance that provides protein, an essential nutrient for the body. Proteins are made up of amino acids, which are vital for building and repairing tissues, making enzymes, and supporting immune function. Common protein sources include meat, fish, dairy products, eggs, and plant-based options like beans, lentils, and tofu. Different protein sources vary in their amino acid profiles and nutritional content. Animal-based proteins typically contain all essential amino acids, making them complete proteins, while many plant-based proteins may lack one or more essential amino acids, classifying them as incomplete proteins. Combining different plant sources can help achieve a balanced intake of amino acids.