**1. Introduction**

Uremic toxins are substances produced by protein metabolism. In persons with chronic kidney disease (CKD), these substances can accumulate and contribute to the diversity of symptoms produced by end-stage kidney disease.

In the gut, protein metabolism by bacteria produces ammonia, in the presence of urease enzymes. Diet has an important role, as animal protein generates more uremic toxins than vegetable proteins. Also, microbial fermentation of some amino acids and gut microbes can generate uremic toxins.

Patients with advanced chronic kidney disease in pre-dialysis and patients in renal replacement therapy need an adequate balance of protein in the diet, since dialysis can remove some uremic toxins, but not all and studies suggest that these toxins can contribute to cardiovascular risk and mortality.
