June/July 2021 Issue
MNT in Chronic Kidney Disease
By Jamie Santa Cruz
Vol. 23, No. 6, P. 40
Targeted, individualized nutrition can help slow and even prevent the condition in patients.
Approximately 15% of American adults—37 million people—have chronic kidney disease (CKD). Incidence of the disease is growing in tandem with America’s aging population and rates of obesity.
Since CKD typically doesn’t cause symptoms until the later stages, 9 out of 10 individuals with the disease don’t know they have it—including one-half of those who have very limited kidney function.1 But the disease is serious: CKD is the ninth-leading cause of death in the United States.2
Fortunately, nutritional factors can significantly impact the progression of CKD.3 At a minimum, a careful diet can help preserve patients’ remaining kidney function and treat complications of the disease. In some cases, nutrition also may help patients regain kidney function they’ve previously lost.
Chronic Kidney Disease: An Introduction
CKD is most common in adults older than 65, but a significant percentage of younger adults also suffers from loss of kidney function. Diabetes and high blood pressure are the major causes of CKD, but heart disease, obesity, family history, and past kidney damage also are risk factors. As for the consequences of the disease, CKD is of significant concern because it increases the risk of heart disease and stroke.1 CKD also is linked to a variety of complications, including anemia (which causes weakness and fatigue), weakened bones, arrhythmia, loss of appetite, fluid retention (which causes high blood pressure, swelling in the legs, and shortness of breath), and increased risk of infection.
CKD is classified into five stages based on the extent of kidney function, which is measured by glomerular filtration rate (GFR). In the earlier stages, when GFR is still high, the functioning kidney tissue can increase its performance and thereby compensate for the small amount of nonfunctioning tissue, so there are few obvious adverse effects of the disease.4
Even in the earlier stages, however, loss of kidney function starts affecting the body’s ability to maintain fluid and electrolyte homeostasis. The kidneys gradually begin losing their ability to concentrate urine, and as the disease progresses they also begin losing the ability to excrete excess phosphorus, potassium, and acid. In end-stage kidney disease (renal failure), the kidneys are unable to concentrate or dilute urine, and increasing water intake no longer leads to increased urine output.4
Dialysis is necessary in end-stage renal failure—usually once 85% to 90% of kidney function is lost and GFR falls to less than 15.5 There are two types of dialysis available for people with CKD. Hemodialysis, which is the more common, involves removing the blood from the body and then using an artificial kidney to filter it and remove waste and excess fluid.
For the other type, peritoneal dialysis, the patient undergoes surgery to implant a peritoneal dialysis abdominal catheter, which filters blood through the peritoneum membrane in the abdomen. During these treatments, a fluid called dialysate is inserted via the catheter into the abdomen, where it absorbs waste before being drained back out of the abdomen through the catheter.
Nutrition and Kidney Disease
Currently, only 10% of patients with kidney disease see a dietitian before reaching end-stage renal failure and undergoing dialysis.3 However, because nutrition has a strong impact on the progression of CKD, the National Kidney Foundation recommends MNT to all individuals with kidney disease, regardless of the stage of disease.6
Historically, the main goal of renal nutrition was simply to prevent complications that frequently accompany kidney disease, such as anemia, hyperkalemia, hyperphosphatemia, and uncontrolled blood pressure, according to Michele Crosmer, RD, CSR, a renal dietitian in private practice in Upland, California, and owner of PlantBasedKidneys.com. That goal remains important, but recently it has become clear that nutrition can slow or halt the progression of the disease itself. Thus, a major goal of nutrition therapy now is to preserve—and in some cases even improve—kidney function.
“Nutrition is the cornerstone treatment of good kidney care, period,” says Jessianna Saville, MS, RDN, LDN, a renal dietitian in private practice in Bryan, Texas, and owner of KidneyRD.com. “It is a game changer. We regularly see that people will improve their GFRs. People say, ‘Once you lose kidney function, you’ll never get it back.’ But that’s not what we see. It’s also not consistent with the literature. […] For people who are really late stage, they can prolong the life of their kidneys and go straight from CKD to transplant instead of having that mid step of dialysis.”
Importance of the Overall Dietary Pattern
Traditionally, the field of renal nutrition has focused heavily on regulating individual nutrients—especially protein, sodium, phosphorus, and potassium. Unfortunately, focusing exclusively on individual nutrients meant patients with CKD have tended to reduce intake of healthful foods, such as leafy greens, strawberries, bananas, and oranges, that would help keep their chronic disease in check while increasing consumption of less healthful foods, such as refined grains, in an attempt to avoid a particular micronutrient such as potassium.
For this reason, an increasing number of researchers and renal dietitians are arguing for greater attention to the patient’s dietary pattern as a whole.7,8 “Yes, we have to look at individual nutrients and make individualized recommendations on those,” Crosmer says. But “one of the biggest nutritional considerations—before you look at specific nutrients—is getting away from that standard American diet and looking at the overall quality of diet: What foods are they eating, what are they cooking, how many fruits and vegetables are they taking in, are they eating out a lot, are they eating a lot of processed food?”
Several different healthful dietary patterns have received attention for their potential to help protect kidney health, including the DASH diet, Mediterranean-style diets, and plant-based diets. Almost no randomized trials are available, but several of these healthful dietary patterns have been correlated in observational studies with lower risk of incident CKD, slower declines in kidney function, and lower mortality.8-16 To date, there’s no conclusive evidence about whether one particular dietary pattern should be recommended over another, but all the dietary patterns that appear to show evidence of benefit have a few things in common: All emphasize fruits, vegetables, whole grains, and legumes while limiting intake of red meat, sodium, and refined sugar.
Regardless of which healthful dietary pattern a patient with CKD follows, dietitians should be prepared to tailor the diet based on the patient’s stage of disease. The DASH, Mediterranean, and plant-based diets all tend to be high in phosphorus and potassium, which can be problematic for some patients with CKD. “In earlier stages, [these diets] are great, until you get to stages 4 and 5 and dialysis, then you really need a dietitian to help navigate those and personalize,” Gradney says.
The most important nutritional considerations in CKD include the following.
Traditionally, a key focus of the standard renal diet has been minimizing protein. This is because higher protein intake induces hyperfiltration in the kidneys (a temporary overworking of the kidneys) and a consequent increased excretion of albumin in the urine, which are thought to negatively impact kidney function over the long term.17
The Modification of Diet in Renal Disease (MDRD) trial, which is the largest randomized controlled trial to examine protein restriction in CKD, raised questions about the value of restricting protein because the study failed to show a clear benefit of consuming a low-protein diet for slowing CKD progression.18 Other research, meanwhile, raised concern that a diet too low in protein can increase the risk of protein-energy wasting.17
However, multiple other trials before and after MDRD—and secondary analyses of the data from MDRD alone—suggest that a diet low in protein remains an important strategy for treating CKD.7 The current guidelines of the National Kidney Foundation recommend that individuals with stage 3 to 5 kidney disease who don’t have diabetes and aren’t on dialysis should keep protein consumption to 0.6 g/kg of body weight per day (the limits are greater than 0.6 g/kg for individuals with diabetes or those on dialysis).6
Although in the past the emphasis in CKD has been on the quantity of protein, there’s now an increasing focus on how the quality of protein affects the disease, and many renal dietitians now encourage patients with CKD to consume plant proteins over animal proteins. While animal-based protein is known to prompt hyperfiltration in the kidneys, plant protein doesn’t cause the same stress. Diets higher in plant-based protein also are linked to greater decreases in blood pressure—an important concern given that high blood pressure reduces blood flow to the kidneys and contributes to loss of kidney function.7 Other evidence suggests that diets with a higher percentage of protein from plants are linked to lower mortality in CKD, implying that both quantity and quality matter.19
Restrictions on sodium intake are widely considered critical for preserving kidney function in CKD, in large part because of the connection between sodium intake and hypertension. 20 Hypertension is a cause of CKD because it impedes blood flow to the kidneys, but it’s also a consequence of CKD because poor kidney function results in reduced sodium excretion in the urine.6 In addition, sodium reduction is important because it reduces proteinuria, which is the excretion of protein into the urine.20 The guidelines of the National Kidney Foundation recommend individuals with CKD keep sodium consumption to less than 2,300 mg per day.6
Potassium and Phosphorus
While protein and sodium intake are of concern even in early stages of CKD, potassium and phosphorus often don’t become an issue until later. If the kidneys lose the ability to clear excess potassium and phosphorus, these nutrients can build up in the blood, resulting in complications such as muscle weakness, hypertension, arrhythmias, bone disorders, and problems with mineral metabolism.6
In the past, it was standard practice to encourage all individuals with kidney disease to restrict potassium and phosphorus. However, the current guidelines of the National Kidney Foundation don’t make an across-the-board recommendation to avoid either nutrient, stating instead that dietary advice on restriction of these nutrients must be individualized. “I’ve worked with people with 5% kidney function with no potassium issues and don’t have a restriction, and I’ve worked with people at stage 3 with 50% kidney function and they have high potassium and need to limit it,” Crosmer says.
According to Crosmer, dietitians should be conscious of the fact many patients with CKD over restrict in making dietary changes because they have a fear of a particular nutrient. “People will come and be like, ‘OK, I have kidney disease, I have to stop eating potassium,’ and so they stop eating all these beneficial whole plant foods that can actually help protect their kidneys,” Crosmer says. Even if patients need to restrict potassium, she says, it’s important to help them identify ways to eat plenty of lower-potassium fruits and vegetables.
Alkalinity of the Diet
Increased intake of fruits and vegetables also are encouraged to boost alkalinity. Diets that are more acidic have been linked to low albumin, muscle wasting, bone disease, and more rapid progression of CKD.21 Therefore, maintaining alkalinity is critical in kidney disease, and eating a plant-heavy diet is a key strategy for achieving this goal. Animal proteins create large amounts of acid in the body; by contrast, plant-based proteins are far more alkaline, and intake of fruits and vegetables is linked to reduced acidosis in CKD.7,22
Gut health is closely linked to kidney disease. With the progression of CKD, urea starts to accumulate in the blood, causing alterations in the gut microbiome that can stimulate the production of toxins in the gut. These toxins, in turn, alter the epithelial barrier and can accelerate injury to the kidneys.23 “It doesn’t matter what stage you are; it’s incredibly, incredibly important to understand gut healing and good gut health,” Saville says.
To promote gut health in kidney disease, Saville recommends supplementation with prebiotics, probiotics, and digestive enzymes as appropriate based on specific digestive symptoms the patient is experiencing. However, these supplements shouldn’t necessarily be permanent for patients with CKD. “All supplements […] are like scaffolding on a house. [They’re] meant to support healing and [an] optimal health process, and after that they’re meant to be taken down and supported by diet,” Saville says. “A lot of people can come off of these. If their diet is robust and full of a variety of fruits and vegetables, [which are prebiotics and that often contain natural digestive enzymes,] I think it’s a great thing to pull off [supplements] or at least use [them] periodically.”
Another significant way to promote gut health is to increase fiber intake. Individuals with CKD tend to have chronically low consumption of dietary fiber, in large part because of the effort to avoid potassium and phosphorus. However, fiber improves the composition of gut microbiota, thereby reducing production of uremic toxins and potentially helping to stem CKD progression.24 A 2015 meta-analysis found that increased fiber intake in individuals with CKD was linked to beneficial reductions in serum urea and creatinine—both of which are classical biomarkers of kidney function.25 Aside from promoting gut health, fiber intake also is well known to help manage diabetes and lower CVD risk, which is significant because CVD is the major cause of death in patients on hemodialysis.7,26
As far as sources of fiber to recommend, “fruits and vegetables are great,” says Kristen Gradney, MHA, RDN, LDN, senior director of operations at Our Lady of the Lake Children’s Health in Baton Rouge, Louisiana, and a spokesperson for the Academy of Nutrition and Dietetics. “We always share lists [of fruits and vegetables] that are low potassium and low phosphorus.” In the beginning stages, she says, it’s also permissible and even advisable to eat whole grains, such as whole grain bread and brown rice. “If you’re consuming those early on, that can help improve your diabetes, your hypertension, your high cholesterol, which could slow the progression of renal failure.” For patients who aren’t receiving enough fiber from food, fiber supplements also are acceptable for boosting fiber intake, Gradney says.
In addition to fiber, many patients with CKD need various micronutrient supplements as the disease progresses, according to Gradney. “Vitamin D is typically the one that we are really concerned about. Chronic kidney disease patients are at risk of secondary hyperparathyroidism, and we normally supplement with vitamin D to combat that.” Saville also encourages dietitians to monitor levels of selenium (which can be too low) and iodine (which can be either too high or low), since these two micronutrients also are important for thyroid health in patients with CKD.28,29
Moreover, anemia is a common issue in CKD. Anemia affects almost all patients with CKD in the later stages of the disease,18 but according to Saville it also can crop up in earlier stages. Anemia in CKD has multiple causes, but iron deficiency is one contributor, so iron supplements (often given intravenously) are a necessity for many people.8
Accurate nutritional assessments are critical for patients with CKD, according to Saville, because nutrition needs vary significantly from patient to patient and from one stage of the disease to the next.
“There’s not one [single] renal diet,” Saville says. “Some people need high potassium or don’t need to worry about phosphorus. […] Nutrition assessment and understanding pathophysiology of nutrient restriction is really critical. Nutrient assessment for kidneys must always be driven by labs, underlying cause of kidney function, and comorbidities. If you give everyone with kidney disease the same diet, then you’ve missed a piece,” Saville says.
It’s important to do at least two nutrition assessments per year, Gradney says, because the disease can progress. When assessing nutrition, dietitians should make sure they look at the larger context of the patient’s access to food. “What I find a lot in dialysis clinics is that patients have really limited access, and so they’re eating foods that are increasing their phosphorus and potassium because that’s what they have.” In many cases, Gradney says, limited food access stems from the fact patients live in high-priority food areas (formerly termed “food deserts”); in other cases, the issue may be that patients are dependent on family members to shop for them. “You find that out through assessments. So it’s more than just assessing the biochemical marker; it’s really assessing the social determinants of health as well,” she says, adding that when necessary, dietitians should involve a social worker to help patients overcome challenges of food access.
Crosmer has two closing challenges for fellow dietitians: First, be ready to alert patients to kidney disease if no one else is doing so. “I’ve worked with people who came in to me for diabetes and I’m looking at their labs and they have stage 3 kidney disease and their doctor’s not saying anything. So we can be that advocate [and say,] ‘Hey, talk to your doctor about your labs,’ [so] they’re aware of kidney disease early on.”
The other challenge? Believe in the patient. “We don’t [always] have faith that someone will make an extreme change, so we don’t make that recommendation, and I think we’re kind of doing a disservice when we do that. We need to have faith that dialysis is a scary thing, and people will do almost anything to prevent it,” Crosmer says. “If they hear from their doctor, ‘This is progressive, there’s nothing you can do,’ [implying that] diet doesn’t matter that much, we can be that advocate and say, ‘Yes, it does, it makes a huge difference, and you can slow or prevent the progression of kidney disease with medical nutrition therapy.’”
— Jamie Santa Cruz is a health and medical writer in Parker, Colorado.
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