Kidneys role is to filter waste and toxins from the blood, and maintain the normal balance of fluid and minerals within the body. As pets are getting older, damage to kidney tissues may occur.  This process is irreversible, and will lead to further loss of kidney function.  Renal dogs may also experience loss of appetite and their caloric intake might decline, which may lead eventually to loss of muscle mass.Hill's nutritionists and veterinarians developed Prescription Diet® k/d®, clinical nutrition to support your dog's kidney health. In fact, The nutrition of Prescription Diet® k/d® is clinically proven to improve & lengthen quality of life.