According to Kidney Facts, urea is the major waste product that results from the metabolism of protein. Urea makes up nearly half of the total urinary waste that the body passes.
Kidney Facts says that since most of the urea in the body is removed via urine, doctors take urine samples to determine how much protein an individual has in his diet. Uric acid and ammonia are other common waste products that come from protein metabolism, and the kidneys also excrete minerals like sodium, calcium and magnesium. The kidneys can adapt from getting virtually zero grams of sodium to 25 grams per day.