Nutritional Intervention in Chronic Kidney Disease

DIETARY PROTEIN RESTRICTION has been prescribed in chronic kidney disease (CKD) for a century, and a low-protein diet (LPD) or supplemented very low-protein diet with ketoanalogs of amino acids (SVLPD) has been prescribed for four decades. It was argued that such a regimen may be associated with a deterioration of nutritional status. Such intervention is uncommon now in the United States and in most European countries, in which a standard diet with 0.8 g/kg/day of protein is commonly used. At the same time, most patients present signs of protein-energy malnutrition at the start of renal replacement therapy (RRT), even if they have consulted a nephrologist in the preceding months or years. The Comprehensive Dialysis Study, which is part the United States Renal Data System (USRDS) 2008 data report, involved a special collection of data on the nutrition, activity, and quality of life of patients who initiated RRT between 2005 and 2007. The first results showed that at the start of RRT, 60% of patients exhibited a serum albumin level lower than 35 g/L, and in 80% of these patients, the alimentary intake was below the actual recommendations.1

In contrast, during the last several decades, no study demonstrated that LPD or SVLPD was associated with malnutrition. The first and second analyses of the Modification of Diet in Renal Diseases (MDRD)-Study concluded that such a regimen is safe in uncomplicated and carefully monitored cases. Short-term follow-up of SVLPD patients showed no adverse nutritional effects after patients started dialysis, or during and after transplantation. One could object that these patients were carefully selected and monitored. This last point is important, because a nutritional survey should be the main feature of an adequate, long-term follow-up of CKD patients before RRT. The implementation of nutritional guidelines is associated with better results.2 A review of the literature regarding protein intake and CKD confirmed that nutritional therapy is effective to reduce comorbidities associated with CKD: nutrition, phosphate intake, proteinuria, and cardiovascular risk factors.

All the reports from this symposium demonstrate that nutritional intervention in CKD patients is not an outmoded therapy based on antiquated clinical studies, and that a supplemented, protein-restricted diet has its place in a therapeutic approach. The long-term follow-up of patients in previous studies confirmed the safety and nutritional adequacy of these diets, and recent clinical studies of nondiabetic and diabetic patients led to the same conclusions. The experimental and clinical studies reported in this issue of the Journal illustrate all the mechanisms (and new directions) involved in the beneficial effects of LPDs supplemented with keto acids/amino acids: the effects on proteinuria and endothelial dysfunction, specific effects of branched-chain amino acids, effects of keto acids/amino acids on asymmetric dimethylarginine and body fat mass, and effects on glomerular structure and renal fibrosis. Clinical studies confirm previous studies and meta-analyses: SVLPDs delay the time to RRT, and could be of economic importance. Clinical studies also confirm the positive effects suggested by experimental data in terms of obese transplanted patients, diabetic patients, and the preservation of renal function in peritoneal dialysis patients. To help nephrologists and dietitians, the expert panel proposes a consensus statement on keto acid therapy in diabetic or nondiabetic predialysis patients and in nephrotic syndrome.

In conclusion, nutritional interventions and specifically supplemented very low protein diets have many proven advantages in terms of the progression of renal failure, better metabolic and endocrine control, and decreased proteinuria. Patients are in need of a detailed nutritional survey by dietitians and nephrologists. This should be the case for all CKD patients, but especially for SVLPD patients, to avoid malnutrition. Toward this goal, all the data reported in this issue by international experts on this topic will help… and will offer some new directions for future research.