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.
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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.