Update of dietary management in chronic kidney disease patients

The kidney is responsible for the excretion of body water, uremic toxins, phosphorus, postassium, and acid. Patients with chronic kidney disease (CKD) shouldn't depend on medical treatment, but should put more emphasis on dietary management instead. Mediterranean diet is rich in dietary fiber and fructo-oligosaccharides, i.e. the prebiotics, which are consumed by the healthy gut microbial flora. These beneficial microorganisms, i.e. the probiotics, produce short-chain fatty acids via saccharolysis, a process of fermentation, and create an environment of microbial symbiosis in human gut. Of note, the vegetables and fruits which Mediterranean diet highlights are rich in potassium. Therefore, vegetables should be pre-treated by boiling in water before ingestion, and fruits should be properly selected to ensure sufficient dietary fiber intake in patients with advanced CKD, instead of directly avoiding potassium-rich foods. Grains, nuts, and yogurt, which are also key elements of Mediterranean diet, contain plenty of organic phosphorus and should be restricted in patients with advanced CKD. However, it's even more essential to avoid the exposure of inorganic phosphorus, which usually exists in processed foods. In contrast to Mediterranean diet, Western diet lacks dietary fiber and is characterized by red meat, animal fat, sweetened food, and salts instead, which might result in gut microbial dysbiosis. Of note, the amino acid tryptophan is consumed by the gut microbial flora, which produces indole through proteolysis, a process of putrefaction. Indole is then absorbed via gut villi and enters the portal system of liver, where it is then sulfated and metabolized into indoxyl sulfate. Indoxyl sulfate is a protein-bound small molecule uremic toxin and is harmful to various cells, particularly vascular endothelial cells. In CKD patients, the excretion of indoxyl sulfate is impaired, and it is thus accumulated in the body and leads to a vicious cycle. In conclusion, CKD patients are at risks for gut dysbiosis, partly results from dietary restrictions of potassium and/or phosphorus. An integrative care involving comprehensive dietary instruction allows CKD patients to ensure dietary fiber intake, which might be beneficial not only for gut peristalsis but also to restore gut microbial symbiosis.