Hill's Prescription Diet k/d Feline The kidneys filter waste and toxins from the blood and maintain the normal balance of fluid and minerals within the body. As pets age, damage to kidney tissues may occur. This process is irreversible and leads to loss of kidney function. Cats with decreased kidney function may experience loss of appetite and their food intake might decline, which may lead to loss of muscle mass. Hill's nutritionists and veterinarians developed Prescription Diet k/d clinical nutrition to support your cat's kidney function and help sustain muscle mass. In fact, the nutrition of k/d is clinically tested nutrition to improve & lengthen quality of life.