Protein is important for helping to build and repair tissues and for muscle strength. To name a few, protein also aids in weight management, lean body mass, and supports a healthy immune system. The vast majority of protein products are sold as powders to be mixed with water or milk. Most of them contain, as their principal ingredient, milk protein (whey protein and/or casein) but egg and soy proteins are also fairly common. These products are designed to be a convenient source of high-quality protein to meet the well-established increased needs of athletes and individuals who participate in heavy exercise.