Splanchnic tissues play a crucial role in uremic glucose intolerance

Do low-protein diets work in chronic kidney disease patients?

Patients with chronic kidney disease have been advised for many years to reduce their protein intake. This review addresses the biochemical, pathophysiologic, and nutritional background that underlies this recommendation. The clinical and therapeutic evidence for prescribing such diets is addressed, as well as the potential caveats. A proposed method for managing and monitoring patients also is provided.

Eleven reasons to control the protein intake of patients with chronic kidney disease

For many years patients with chronic kidney disease have been advised to control the protein content of their diet. This advice has been given on the basis of a number of reported metabolic effects of lowering protein intake, such as lowering serum urea nitrogen levels, improving phosphocalcic metabolism and insulin resistance and, more recently, ameliorating proteinuria (independent of antiproteinuric medications). The effects on the progression of kidney disease, although spectacular in experimental studies, have been less convincing in humans. It is possible that flawed design of clinical trials is responsible for this discrepancy. In this Review, we comment on experimental findings that indicate that limiting protein intake protects the kidney and ameliorates uremic symptoms, outline how the body adapts to a reduction in protein intake, and describe the metabolic benefits to the patient. We then review the evidence from randomized controlled trials and meta-analyses that pertains to the effects of low-protein diets in adults with chronic kidney disease.

Carbohydrate metabolism in uraemia

PURPOSE OF REVIEW

Most uraemic patients are insulin resistant. This review focuses on the occurrence, mechanisms and consequences of this insulin resistance. Hypoglycaemia is also possible in a minority of uraemic patients; its causes are discussed at the end of the review.

RECENT FINDINGS

Insulin resistance is detectable when the glomerular filtration rate is below 50 ml/min per 1.73 m in non-diabetic uraemic individuals. Uraemia can alter insulin sensitivity even in diabetic patients; familial insulin resistance may favour the occurrence of diabetic nephropathy. Although reduced glucose non-oxidative disposal is the most evident defect of carbohydrate metabolism, abnormal glucose oxidation, endogenous glucose production and insulin secretion are also contributors. The accumulation of nitrogenous compounds is the most important mechanism of a specific state of insulin resistance in uraemia. Their identification is progressing, particularly in the field of carbamoylated amino acids. The consequences of chronic renal failure such as anaemia, metabolic acidosis and secondary hyperparathyroidism also indirectly play a role.

SUMMARY

The treatment of uraemia by renal replacement therapies or low-protein diets improves insulin sensitivity. However, patients still have a high cardiovascular risk. The identification of the accumulating molecular species that specifically alter insulin sensitivity is therefore of great interest. The favourable effect of non-specific insulin sensitizers such as glitazone may also help to reduce this risk.