Diets for Patients With CKD: What's New, What's Best?

Anya Romanowski, MS, RD


March 27, 2019

What is the ideal diet for a patient with kidney disease? Past recommendations were to reduce protein, potassium, phosphorus, sodium, and fluid intake. Have any of the recommendations changed in the past decade? Medscape interviewed Deborah J. Clegg, PhD, the lead investigator of a recent study[1] published in the Clinical Journal of the American Society of Nephrology, that reviewed the potential health benefits of plant-based diets in patients with chronic kidney disease (CKD).

Why Are Plant-Based Diets Best for Patients With CKD?

Medscape: You focused on plant-based versus meat-based diets, and specifically, you compared the Dietary Approaches to Stop Hypertension (DASH) diet with the Mediterranean diet. Is one diet more beneficial for patients with CKD?

Clegg: The benefits of plant-based diets are very similar. Patients with CKD should be encouraged to consume more plant-based proteins as opposed to meat-based proteins. Meat-based diets are typically much more acidic than plant-based diets, and there are health benefits associated with changing the acid-base balance in the diet.

As background, growing evidence supports the health benefits of plant-based diets, such as the DASH diet, which are high in fiber and low in saturated fat; contain sources of potassium, phosphorus, magnesium, calcium; and have low levels of sodium for preventing heart disease and hypertension.[2,3] In contrast to meat-based diets, which are high in full-fat dairy foods as well as higher in sulfur-containing amino acids and phosphate, plant-based diets are lower in these amino acids and lower in bioavailable phosphorus, both of which have been associated with reductions in cardiovascular disease and CKD.[1,2,3,4]

The acid-base balance in the body is a vital aspect of homeostasis. The balance needs to be controlled within a narrow range, and values outside of this range are not compatible with life. Our bodies attempt to maintain a narrow acid-base range by any means necessary. A disturbance of the acid-base balance occurs when acid-base changes surpass the body's ability to regulate it, or when normal regulatory mechanisms become ineffective. This can happen with chronic consumption of an acidic diet.

You can affect the acid-base status of your body with the foods you eat. What determines a food's acidity or alkalinity is how it breaks down when digested. Most of the foods that contain exclusively protein tend to be high in sulfur-containing amino acids, and therefore are considered acidic. Most plant-based foods don't contain high levels of sulfur-containing amino acids and are generally alkaline-forming. The alkaline-forming plant foods help to neutralize the acid-forming protein foods. We benefit from having an even distribution of acid-forming and alkaline-forming foods in the diet. Even consuming slightly more plant-based/alkaline-forming foods (versus acid-forming foods) may be beneficial for long-term health outcomes.

Furthermore, plant-based diets encourage people to eat less processed foods. We underappreciate the fact that most of our meat products are loaded with added citrates, nitrates, and phosphorus. These ingredients are unhealthy for everyone, including people with failing kidneys.

Medscape: Are there any specific foods or micronutrients within a plant-based diet that patients with CKD should avoid?

Clegg: I think it's really important that we focus on potassium levels. We've always talked about reducing sodium in patients' diets, but now the shift is to increase potassium intake and change the potassium-to-sodium ratio to be much healthier. I think it is important for physicians to specifically address this ratio.

Yet, concerns remain about the plant-based diet for people dealing with serious illnesses, such as CKD. Plant-based diets contain sources of potassium (Table), which has many benefits but can be fatal for people with kidney disease if the level of potassium in their blood spikes, a condition known as hyperkalemia.[1,5]

In the United States, more than 3 million patients are living with hyperkalemia. People with such conditions as CKD or heart failure are at highest risk for hyperkalemia.[6,7] Some individuals whose kidneys are not functioning properly and are not able to remove excess potassium, may not be able to maintain a plant-based diet because of the risk for hyperkalemia.[1]

Table. Plant-Based Food Sources of Potassium

  Serving Size Potassium (mg)
Beans (black) 1 cup 2877
Beans (red kidney) 1 cup 2742
Apricots (dried) 1 cup 2202
Peas (green, split) 1 cup 1670
Potatoes (baked) 1 large 1644
Chickpeas 1 cup 1436
Raisins 1 cup 1361
Plantains (yellow) 1 medium 1315
Cocoa powder (unsweetened) 1 cup 1311
Pistachio nuts (roasted) 1 cup 1239
Avocados (California, pureed) 1 cup 1166
Peanuts (raw) 1 cup 1007
Almonds (roasted) 1 cup 984
Spinach (boiled) 1 cup 839
Tomatoes (cooked) 1 cup 523
Orange juice (fresh) 1 cup 496
Banana (raw) 1 medium 422
Source: US Department of Agriculture. USDA Food Composition Databases.

In general, experts recommend eating a diet that contains at least 4700 mg of potassium per day if you have normal, healthy functioning kidneys.[8] However, most people with moderate to severe CKD or acute kidney injury should eat less than 2000 mg of potassium per day. Of note, although these have been the standard guidelines, new data support an individualized approach to potassium restrictions, indicating that some individuals may be able to tolerate more potassium in their diet despite CKD, especially when the source of the potassium is factored in.[9,10] Consumption of fresh fruits and vegetables may be better tolerated and cause less risk for hyperkalemia than meats and processed foods.

Potassium Binders and the Potential for Diet Liberalization

Medscape: Will the newer potassium binders allow patients to consume "forbidden" foods'?

Clegg: We don't like to think of foods as being "forbidden"; there are just foods that need to be consumed in greater moderation. With the new potassium binders, there may be opportunities to consume more fresh fruits and vegetables, even in people with CKD. Current studies are under way to specifically explore diet liberalization in patients with CKD.[9]

Is there a subset of patients on dialysis who could afford to have a more liberalized and enriched diet, one that incorporates more fresh fruits and vegetables?

Our study was supported by Relypsa, Inc (a Vifor Pharma Group company), which is one of several companies that introduced new potassium binders into the market.[1] The real novelty here is incorporating foods that are typically high in potassium back into the renal diet; that is something that, as dietitians, we've long avoided. We've always been afraid of allowing a banana, or another fresh fruit or vegetable, in the diet plan of a patient with CKD, and yet these foods are healthy and provide health benefits beyond being just sources of potassium.

Medscape: Do the dietary recommendations differ for patients who are currently receiving dialysis and those who are not?

Clegg: This is a phenomenally interesting question. I had the opportunity to attend a meeting on the management of hyperkalemia at the Kidney Disease Improving Global Outcomes (KDIGO) conference. We chronically restrict potassium intake in patients with kidney disease, but we found that the data for patients on dialysis are sketchy. When you actually look at the literature, there are studies showing that despite an increase in potassium intake, there was no significant increase in plasma potassium levels, even though the patients were on dialysis.[11,12]

This is an emerging area that we want physicians to be aware of and start thinking about. Is there a subset of patients on dialysis who could afford to have a more liberalized and enriched diet, one that incorporates more fresh fruits and vegetables? This might not work for everyone, because some patients have chronically elevated potassium levels and hyperkalemia can be lethal, but there may be a subset of individuals who can tolerate diet liberalization without rises in serum potassium.

Phosphorus Absorption and Diet Recommendations

Medscape: Has there been any talk or focus on phosphorus intake in patients with CKD?

Clegg: Yes. There's been more attention on phosphorus than on potassium. Studies have shown that the phosphorus in foods consumed on a plant-based diet is less readily absorbed than phosphorus from animal sources.[13] Patients who consume primarily meat products have an increased risk for hyperphosphatemia. It takes us back to focusing on plant-based diets and utilizing them as a way of managing urine phosphorus excretion.

Certain potassium-containing foods (nuts, legumes, beans, and dairy products) also contain phosphorus. Phosphorus occurs in two forms: organic (as phosphates) and inorganic (as salts). In general, organic phosphorus is naturally found in food, whereas inorganic phosphorus salts are added to foods for purposes of moisture retention, longer shelf life, and enhanced flavor. The absorption of phosphorus from the plant-based foods that contain organic phosphorus (and potassium) is less than 50%, owing to the phytic acid content. Organic phosphorus in plant-based foods is mostly in the storage form of phytates or phytic acid, and humans do not possess the enzyme required to degrade phytates or phytic acid; thus, the bioavailability of phosphorus from plant-based sources is low. Therefore, although high in phosphorus, plant-based foods do not significantly contribute to serum phosphorus levels compared with inorganic phosphorus from food additives and phosphorus from animal-based sources, which contribute significantly to serum phosphorus levels.

Because of the importance of avoiding high serum phosphorus levels, patients on dialysis are required to take phosphate binders. These binders contribute to the high pill burden experienced by people on dialysis and can contribute to constipation, which in term reduces fecal excretion of potassium. A diet that is plant-based and high in organic phosphorus-containing and potassium-containing foods could ultimately contribute to a reduced daily pill burden, owing to the reduced phosphorus bioavailability and lack of significant contribution to serum phosphorus levels.

Alkaline Diet: An Alternative to the Renal Diet?

Medscape: In 2017, researchers suggested that following an alkaline diet might improve the health of patients with CKD.[14] What are your thoughts on this diet?

Clegg: What they're basically saying is an alkaline diet is much more analogous to the DASH or other plant-based diets. So it's avoiding meats and getting more plant-based proteins into the diet.

I think that we oftentimes confuse patients because we call all these diets by different names, but they are one and the same. Researchers are finding significant benefits of plant-based diets in lowering the risk for cardiovascular disease, diabetes, and kidney disease.[1,2,3,4] We're really focusing on going back to the basics of eating fresher and less processed foods.

Medscape: It's difficult to control and measure what a person actually eats, and often the data are self-reported. It's not like studying the effects of a drug, where you have a control group of patients who are on a certain drug and another group that is not.

In your opinion, what diet studies should we be focusing on for renal patients?

Clegg: As a dietitian, I seldom went back to the actual literature and looked for well-designed, randomized, controlled studies to look at the influence of diet on CKD. I just made the assumption, as everyone does, that protein, phosphorus, and potassium are bad. We need to go back and do a lot more research to begin to change that dogma, peel that onion back, and find the pockets of patients with CKD who do well on more liberalized plant-based diets.

Patients on dialysis are often chronically constipated. We give them all these binders and drugs. Now there is some suggestion that the colon and the gastrointestinal tract might be able to sense and facilitate body homeostasis of potassium. There's even talk that perhaps when the kidney begins to fail, there are other organs in the body, such as the gastrointestinal tract, that take over the job of regulating potassium homeostasis. If we provide fruits and vegetables to patients to relieve some of their constipation, will it also reduce their fluctuations in potassium when they are on dialysis? This topic calls for more studies to be conducted.

To specifically answer your question, we need more studies focusing on the health benefits of plant-based diets in people with CKD. These need to be randomized controlled trials under physician and dietitian supervision. Yes, diet recalls are difficult, but it is a start—and if we educate the patients of the importance of these studies and their potential impact on their health and well-being, we might be able to truly determine the best, most nutritious health plan for people with CKD.

Medscape: In the past, we recommended and encouraged patients to consume more fiber to regulate their bowel movements and avoid constipation. Any thoughts on fiber intake for patients with CKD?

Clegg: I couldn't agree more! As previously mentioned, there are new data supporting a role of the gastrointestinal tract in regulating potassium homeostasis. Increasing bowel movements is exactly what we should be focusing on for patients with CKD. I think it's a combinatorial effect, in that we provide patients medications which cause constipation while at the same time, we tell them to reduce their intake of fresh fruits and vegetables and even to boil their vegetables, which reduces the potassium content but also the fiber content. We even tell our patients with CKD to avoid high-fiber breads because of the phosphorus. Basically, we are giving diets that create constipation.

Again, we need to go back and revisit the diet recommendations, and begin to focus on liberalization/individualization of the diet to see whether we can incorporate more fiber-rich foods that take advantage of the gastrointestinal tract's role in potassium homeostasis and perhaps begin to learn about the role of the gut microbiota in health benefits of patients with CKD.

Thoughts on Dietary Supplements and Processed Foods

Medscape: Should patients with CKD take any dietary supplements?

Clegg: I am against supplements and prefer that patients get their necessary nutrients from food sources. However, patients should talk to their doctor to see what works best for them. Many supplements contain products not listed on the label, which may interfere with other medications that individuals are taking.

Medscape: Dietary supplements are under different regulations than drugs, and are considered safe until proven otherwise. There are a lot of impurities and additives in supplements; some even contain stimulants.[15,16] You're pulling nutrients from a natural food source and trying to replicate the health benefits in a pill form.

Clegg: I also worry about drug-nutrient interactions in patients with CKD, because they are often prescribed multiple drugs. Knowing what undisclosed ingredients are in the supplements you're taking and whether any constituents might lead to a drug interaction is very concerning.

Medscape: We have the same concern about processed foods. We need to pay closer attention to how the foods are processed, and what types of preservatives and additives are in the food.

As far as beverages and fluid intake, which was always a concern with patients with CKD, have recommendations changed?

Clegg: Fluid restriction is another component of the diet that patients find incredibly difficult to follow. As we move patients to a DASH diet and away from processed foods, that would lead to a natural reduction in the amount of sodium they consume. Then perhaps the fluid restrictions could be liberalized. Each individual comes in with different analytical weight gains from fluid in between dialysis treatments, and this can be due to actual fluid consumed, sodium content of the diet, or constipation. To get the nutrient benefits of a plant-based diet, I would recommend consuming fruits and vegetables in their natural state and avoiding juices, which provide more fluid.

Suggestions for Physicians Counseling Patients on Diet

Medscape: Any final thoughts or comments that you would like to share with physicians in regards to the dietary needs of patients with CKD?

Clegg: Now is the time for clinicians to see whether they can liberalize the diet in some patients with kidney disease. Physicians should work with dietitians and try to incorporate fresh fruits and vegetables into the patient's diet and then closely monitor their serum potassium levels for any signs of hyperkalemia. Again, potassium binders may allow patients with CKD who are at risk for hyperkalemia to also benefit from a plant-based diet.

In attending the KDIGO meeting, it was exciting to hear physicians say, "We really need to work with dietitians and see whether the diets we're prescribing for patients with CKD have merit and whether more research is needed in order to provide the most accurate healthy dietary recommendations." Some physicians have actually attempted to follow the diet recommendations for patients with CKD and found that dietary compliance is incredibly difficult to sustain; these physicians found the diet to be "boring, bland, and horrible"!

Liberalization of the diet will provide benefit to patients with CKD, because it will allow more food options to be consumed and will enhance overall well-being. Of note, liberalization of the diet will provide more than just the health benefits associated with the diet, but will also offer a higher quality of life.

Additional Resources

Nutrition guidelines for stage 1-4 kidney disease and downloadable patient brochures are available on the National Kidney Foundation (NKF) website. The NKF also provides  guidelines for patients on dialysis.

The US National Kidney Disease Education Program offers  downloadable patient brochures on chronic kidney disease in English, Spanish, and French.

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