New And Proper Approaches to the Kidney Diet

According to the Centers for Disease Control and Prevention, more than 15% of adults in the United States have chronic kidney disease — approximately 37 million people. Until recently, CKD nutrition guidelines focused more on limiting certain nutrients, such as sodium, phosphorous and potassium. Because of this, many plant foods including fruits, vegetables and whole grains, which are higher in these nutrients, were often restricted for people with CKD.

However, recent research and newer guidelines, such as the National Kidney Foundation’s 2020 Kidney Disease Outcomes Quality Initiative (KDOQI) Clinical Practice Guideline for Nutrition in CKD, created in partnership with the Academy, recommend focusing on total diet quality — which includes more plant foods. This approach, along with an individualized nutrition intervention, may be more effective at slowing progression of CKD than sticking to strict nutrient ranges.

Some research suggests eating patterns associated with better kidney health outcomes include the Mediterranean, DASH, Nordic and vegan and vegetarian diets, all of which place heavy emphasis on plant foods. People adhering to these eating patterns tend to have less incidence of CKD. What’s more, when individuals with CKD adopt these eating patterns, their disease progression often slows.

Plant Versus Animal Protein

The KDOQI guidelines and Academy’s Evidence Analysis Library support reduced protein consumption and close monitoring for adults with CKD stages 3 through 5 who are “metabolically stable” and not receiving dialysis. But while both state there is insufficient evidence to recommend one protein source over another — meaning animal versus plant protein — there may be reason to give this another look, since the guidelines are based upon the best information available as of April 2017 (or through August 2018 for any of the consensus opinion statements).

“While there was insufficient data to support a strong recommendation at that time, additional evidence favoring plant-based proteins has been published since,” says Annamarie Rodriguez, RDN, LD, FAND, who has been a nephrology dietitian for almost 25 years and has served on several boards of renal-related groups and held positions in Academy and affiliate groups. She works full time with an infusion company and runs a private practice.

Regardless, there is enough evidence to support the benefits of incorporating more plant foods and plant proteins for patients or clients with CKD or at risk for CKD, whether plant proteins are the basis of protein consumption or not.

Benefits of Plant Foods for CKD

Potential benefits of plant protein consumption and a plant-based diet for people with CKD may include decreased inflammation, less uremic toxins, reduced metabolic acidosis, improved gut microbiome from increased fiber intake and reduced bioavailability of certain nutrients such as phosphorus and potassium.

Inflammation

People with CKD are at higher risk of inflammation and inflammatory comorbid conditions. For instance, 40% of people with CKD also have Type 2 diabetes; 65% also have cardiovascular disease, and 50% to 75% have hypertension. Cardiovascular disease is the primary cause of death for people with CKD.

Diets higher in plant foods such as the Mediterranean, DASH and vegan and vegetarian diets have been associated with lower comorbidities and inflammation. A 2019 study found eating at least 800 grams of fruits and vegetables per day, or about five servings, showed heart-protective benefits. Furthermore, Rodriguez says there are dozens of epidemiological studies to suggest the protective and anti-inflammatory benefits of increased fruit and vegetable consumption.

“The phytochemicals and antioxidants in fruits and vegetables are so essential to what our patients need when we look at the comorbid conditions and inflammatory response mechanisms that are triggered with CKD,” Rodriguez says. “Eating an abundance of fruits and vegetables is the more natural way to combat that.”

Metabolic Acidosis

Metabolic acidosis, or the buildup of too many acids in the blood, can be both a contributor and a consequence of CKD, occurring because of the kidney’s reduced ability to filter and eliminate acids through urine. Too much acid in body fluids can lead to osteoporosis, insulin resistance and other endocrine disorders, muscle loss or protein energy wasting and worsening kidney disease.

Rodriguez explains that a diet high in animal protein favors acid production due to organic sulfur found in amino acids such as methionine and cysteine, which are oxidized to sulfate. “If we look at plant-based foods such as fruits, vegetables and legumes, they have natural alkaline precursors, such as citrate and malate, which are converted to serum bicarbonate that can act as a buffer.” While there are oral alkali medications, Rodriguez argues that eating a diet high in alkaline foods can be just as effective while providing the benefits of fiber, antioxidants and phytonutrients that are often lacking in the historic or traditional CKD diet.

Reviews in 2013 and 2015 both found a diet higher in fruits and vegetables is beneficial in treating and preventing metabolic acidosis. Randomized controlled trials published in 2012, 2013 and 2014 found eating more fruits and vegetables was as effective as oral sodium bicarbonate for people with CKD stages 2, 3 and 4 with metabolic acidosis.

Rodriguez says even if patients or clients aren’t ready to give up animal-based proteins, finding ways to incorporate more plant foods such as fruits and vegetables may help balance it out.

Bioavailability of Phosphorus and Potassium

Sweeping restrictions of foods high in phosphorus and potassium was once foundational to the CKD diet for people with CKD stages 3 through 5 and on dialysis. This generally resulted in people limiting their consumption of plant foods. However, research suggests the phosphorus and potassium in plant foods are less bioavailable, meaning the body does not absorb all the phosphorus and potassium present in plant sources. A 2018 study adds that animal proteins such as meat, poultry and fish can contain additives of phosphorus and potassium, in a more bioavailable form. The updated KDOQI guidelines suggest practitioners consider bioavailability of phosphorus sources.

“Any time I talk to dietitians about incorporating more plant-based proteins in patients with CKD, they’re more concerned about potassium and phosphorus,” Rodriguez says. She explains that the phosphorus in some plant foods comes in the form of phytic acid, which is largely indigestible in humans because they lack the enzyme phytase, which is needed to convert phytic acid into a more bioavailable form of phosphorus. She says the higher fiber in plant foods may help reduce absorption of both phosphorus and potassium. Additionally, newly introduced potassium binders can help patients and clients keep serum potassium levels within range while also eating more plant foods.

However, processing such as sprouting, fermenting and cooking can make phosphorus more bioavailable, which Rodriguez says she always discusses with her patients or clients. Rodriguez recommends registered dietitian nutritionists educate patients or clients on inorganic sources of phosphorus, which often are found in highly processed foods and beverages such as soda. Virtually all added (or inorganic) phosphorus is absorbed by the body.

RDN Takeaways

Despite the staggering amount of people who have CKD and the potential for medical nutrition therapy to slow the progression of the disease, only 10% of people with non-dialysis CKD are estimated to ever see an RDN. Barriers to MNT may include a lack of physician awareness and referrals, plus RDN availability. Whatever the cause, RDNs may want to consider advocating for the importance of nutrition for CKD whenever possible.

For some people, the cost of seeing a dietitian may be a reason they don’t receive or seek out medical nutrition therapy. To make appointments more affordable, RDNs in private practice could consider becoming Medicare providers, which cover a select number of appointments for beneficiaries with CKD who are not on dialysis or received a kidney transplant within the past 36 months and were referred by a physician.

Patients or clients may have preconceived notions or misconceptions that eating fruits, vegetables and whole grains will have a negative effect on their disease process. When counseling patients or clients, present the updated data and explain the benefits of eating more plant-based foods and create an individualized care plan. If patients or clients are not ready to make big changes, emphasize the impact of small, gradual shifts over time.

“Even small goals, even baby steps, can make a significant impact on health outcomes,” says Rodriguez. “Simple steps, such as swapping out one or two meals a week for a plant-based meal, can really add up.”