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The renal diet is commonly recommended for those with late stages of chronic kidney disease and end-stage kidney disease. The renal diet is characterized by the reduction of dietary sodium, potassium, and phosphorus. The rationale behind these restrictions is to prevent the buildup of these micronutrients in the blood and to reduce complications, such as hypertension, fluid overload, arrhythmias, bone disorders, and vascular calcifications. However, this diet is considered restrictive, hard to prescribe and follow.

A consequence of the renal diet is the reduction in the consumption of some food groups, such as fruits, vegetables, whole grains, legumes, and nuts. These food groups, besides being good sources of the aforementioned nutrients, are also good sources of vitamins, other minerals, polyphenols, and dietary fiber. Indeed, when researchers have looked into the nutrient intake of patients with late stages of chronic kidney disease and end-stage kidney disease undergoing renal replacement therapy (i.e., hemodialysis), patient consumption of some vitamins and dietary fiber is below the recommendations.

Moreover, when dietary patterns have been explored, a predominance of a Western-type dietary pattern with a high consumption of red meat, salt, and refined sugars, and a lower consumption of fruits, vegetables, legumes, whole grains, and nuts has been reported. A Western-type diet may seem counterintuitive as patients with chronic kidney disease have a higher prevalence of cardiovascular disease and mortality than the general population, as well as other comorbidities, such as obesity and diabetes.

The renal diet is restrictive and hard to follow 

But why are patients with chronic kidney disease and end-stage kidney disease consuming a Western-type diet? If you are a registered dietitian, you know that the renal diet is one of the hardest to prescribe. Additionally, often times a patient with kidney disease has other comorbidities, such as diabetes and hypertension, which adds a layer of difficulty to the medical nutrition therapy. Some dietitians provide a list of foods that are high in potassium, phosphorus, and sodium. If you look into the lists of foods, you quickly realize that your options are reduced. Also, some of the cooking methods to reduce these nutrients may require extra time and resources, which could be a barrier for patients and a burden for their care givers. This may lead patients to disregard the recommendations altogether and may be reflected in the nutrient intake and dietary patterns reported. 

The traditional approach to the renal diet is evolving 

The traditional approach to the renal diet is beginning to change. Recently, the European Renal Association-European Dialysis and Transplantation Association recommended the Mediterranean diet as the dietary pattern of choice for chronic kidney disease patients. Additionally, modified and “liberalized” dietary recommendations based on easy-to-follow guidelines have been proposed for hemodialysis patients. However, there may be some healthcare and nutrition professionals who may disagree with these recommendations. One reason is that potassium intake may be increased and a risk of high concentrations of potassium in blood, or hyperkalemia, may outweigh the benefits of the diet overall. However, the association of dietary potassium and serum potassium in end-stage kidney disease patients undergoing hemodialysis treatment is very weak. Moreover, with these dietary patterns most of the phosphorus comes from plant-based foods, as the consumption of animal-based products is limited, which confers a benefit as the bioavailability of phosphorus is lower than the animal sources and the consumption of ultra-processed foods is also limited.

The Mediterranean and DASH-style diet have been associated with reduced cardiovascular and all-cause mortality in the general population. In kidney disease, a dietary pattern that resembles these diets has been associated with a 27% reduction in mortality risk. However, recent results from the DIET-HD multinational cohort of over 8,000 hemodialysis patients showed that a high adherence to the Mediterranean or DASH-type diet was not associated with reduced cardiovascular mortality or all-cause mortality. This study, however, was an observational prospective multinational cohort from European countries using a food frequency questionnaire that uses the British Food Composition Table and, therefore, there is a limited generalizability of the results.  

The nutrition guidelines for patients with chronic kidney disease are being updated

An update for the major nutrition guidelines for kidney disease patients (the Kidney Disease Outcomes Quality Initiative [K/DOQI] guidelines by the National Kidney Foundation) is expected later this year. Even though an overall focus of nutrient recommendations is still expected, it is not known if a particular dietary pattern will be recommended following the recommendations of the European Renal Association-European Dialysis Transplantation Association. Despite this, without a doubt there is a need for prospective, randomized-clinical trials  to provide proof of the benefit on outcomes and quality of life with focusing on dietary patterns rather than mere nutrient restrictions. nd

Many dangerous fad diets exist that purport to treat diseases such as cancer by manipulating the pH of blood with different foods. While there is no good evidence that acidic foods alter the body’s pH and promote disease, the hypothesis that “dietary acid load” relates to disease should not be completely dismissed. The kidney serves to regulate blood pH, but if kidney function declines and other tissues catabolize to maintain pH, then it is very plausible that manipulating the diet to reduce the acid load could spare tissues and improve outcomes in chronic kidney disease (CKD). After all, for example, the metabolism of amino acids yields hydrogen ions, whereas fruits and vegetables contain organic salts that generally reduce acid load when metabolized. Recently, a growing number of human studies that manipulate diet acid load using fruits and vegetables and sodium bicarbonate support this hypothesis. Let’s take a look at some of them.

The first randomized controlled trial on bicarbonate supplementation and CKD progression was published in 2009 by de Brito-Ashurst and colleagues. Bicarbonate is produced by the kidneys and serves to neutralize acid. Supplementation of bicarbonate for 1 year in CKD patients slowed the progression of kidney disease as suggested by creatinine clearance and reduced the need for dialysis. The next year, in 2010, a 5-year trial was published by Donald Wesson’s group that found a slowed kidney decline as measured by estimated glomerular filtration rate (eGFR) with bicarbonate supplementation. Several subsequent studies by his group have used bicarbonate or fruits and vegetables to achieve beneficial outcomes. Goraya et al. gave oral bicarbonate or enough fruits and vegetables that were estimated to reduce dietary acid load by 50% to CKD patients for 30 days and also observed a slowed reduction in eGFR in patients at moderate, but not mild, stages of the disease. In patients with more advanced stages of CKD, one year of bicarbonate or fruits and vegetables did not slow the decrease in eGFR, though several urinary markers of kidney injury were reduced. Their most recent trial tested if kidney function might be preserved through a reduction in angiotensin II in moderate stage CKD patients. Three years of bicarbonate or increased fruits and vegetables lessened the decline in eGFR and resulted in a corresponding decrease in the marker angiotensin II. Other studies using bicarbonate from six months to two years have provided strong evidence that reducing acid load consistently slows the decline of eGFR, and improves markers of bone health and muscle function.

Each of the studies described provided fruits and vegetables to patients free of charge to increase adherence. It will be important to test if adherence can be maintained through education alone. Additionally, it may be that “prescribing” fruits and vegetables is effective at improving outcomes and reducing health care costs more so than bicarbonate since they also reduce blood pressure. While “alkaline diets” in general should be viewed skeptically, there is accumulating evidence that fruits and vegetables as dietary alkali do indeed help in kidney disease.