Diet and the progression of chronic kidney disease

The dietary management of non-dialysed CKD patients has focused on limiting the intake of substances which lead to accumulation of urea, potassium, phosphorus, and sodium. Recent advances in nutritional epidemiology have given us the opportunity to examine the relationships between diet and CKD. This chapter focuses on evidence relating to retarding progression of renal impairment in the early to mid stages of CKD. Limits may need to change if GFR falls. The hypothesis that a high dietary protein intake leads to progressive CKD through a mechanism of glomerular hyperfiltration has been taught for decades, and it appears effective in animals. However, the evidence that low-protein diets (LPDs) halt CKD progression in patients is weak. Their management is of course likely to include other interventions such as blood pressure control. There is risk to low-protein diets. There is some evidence that high protein intakes are harmful. We therefore recommend moderate protein intake (not low; not high – no protein supplements; around 1g/kg/day). Salt handling is impaired in most patients with CKD, probably even early stages, and hypertension is an early feature, except in salt-losing patients, to whom different rules apply. Salt intake tends to raise blood pressure, worsen proteinuria, and reduce the effects of angiotensin converting enzyme inhibitors on blood pressure and proteinuria. Very low salt intakes are difficult to comply with and limit diet. In early stages of CKD we therefore recommend restriction to moderately low levels (below 6g/day of salt; 100 mmol of sodium). Lower levels may have additional benefits, and these limits may need to be reduced as GFR declines. Potassium is associated with healthy, desirable foods such as fruit and vegetables. It should only be restricted if high serum values make this necessary.