Chronic kidney disease (CKD) is a significant global health concern, affecting over 10% of the world's population. The number of individuals impacted by CKD is on the rise, partly due to increasing risk factors like obesity, hypertension, and diabetes mellitus. Diet plays a crucial role in preventing and managing non-communicable diseases, and plant-based diets (PBDs) have garnered attention for their potential health benefits, including protecting against CKD development and progression.
Understanding Plant-Based Diets
The term "plant-based diet" encompasses a range of dietary patterns that emphasize plant-derived foods. However, there is no universally agreed-upon definition. Vegetarian diets fall under this umbrella, including:
- Vegan Diet: A strictly vegetarian diet that excludes all animal products.
- Lacto-Ovo-Vegetarian Diet: Includes small amounts of eggs and/or dairy.
PBDs can also include small amounts of animal products, such as:
- Flexitarian Diet: Accepts all kinds of fresh meat, but only sporadically.
- Semi-Vegetarian Diet: Excludes certain types of meat (e.g., pescatarian, which includes fish, or pollo-vegetarian, which includes chicken).
It's important to distinguish between healthy and unhealthy plant-based foods. Unhealthy options include refined grains, fruit juices, desserts, and potatoes. The rise of ultra-processed plant foods raises concerns about the overall quality and health benefits of vegetarian diets. Studies have shown that adherence to a healthy plant-based diet is associated with a lower risk of CKD, while a less healthy plant-based diet is linked to an elevated risk.
The Academy of Nutrition and Dietetics' Position
The Academy of Nutrition and Dietetics states that appropriately planned vegetarian diets, including vegan diets, are healthful, nutritionally adequate, and may offer health benefits for preventing and treating certain diseases. These diets are associated with a reduced risk of ischemic heart disease, type 2 diabetes, hypertension, certain cancers, and obesity. Furthermore, they are suitable for all stages of the life cycle and are more environmentally sustainable.
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Impact on Diabetes, Hypertension, and Obesity
Diabetes, hypertension, and obesity are major contributors to CKD. Vegetarian diets are linked to a reduced risk of diabetes, dyslipidemia, and ischemic cardiac disease. Switching to a plant-based diet can significantly reduce blood pressure, with vegan diets showing more pronounced effects than lacto-ovo-vegetarian diets. PBDs also have positive effects on body weight, with observational studies indicating that body mass index generally decreases with reduced consumption of animal products, reaching the lowest values among vegans. Interventional studies have demonstrated the effectiveness of plant-based diets, especially vegan diets, in reducing body weight through mechanisms such as reduced caloric intake, improved gut microbiota function, and increased insulin sensitivity. Vegan diets have been found to be effective in reducing body weight. The incidence of diabetes mellitus and metabolic syndrome is also lower in vegetarians compared to omnivores. For diabetics, switching to a vegan diet can improve glycemic control, promote weight loss, reduce the need for diabetes medications, and improve lipid profiles.
Kidney Disease and Plant-Based Diets
Since secondary forms of arterial hypertension, type II diabetes mellitus, and metabolic syndrome are the main causes of kidney disease in industrialized countries, there is a biological basis for linking PBDs with a lower risk of kidney damage. A study involving nearly 15,000 people showed that high adherence to a plant-based diet correlated with a decreased incidence of chronic kidney disease and a reduced decline in kidney function over time. Even in diabetic patients, lacto-ovo-vegetarian and vegan diets are associated with a lower occurrence of CKD. Plant-based diets, particularly those that minimize animal product intake, appear advantageous for the primary prevention of CKD.
Plant-Based Diets and CKD Management
Protein Intake and Kidney Health
High protein intake, especially from animal sources, can lead to elevated intraglomerular pressure and chronic glomerular hypertension, potentially harming kidney health, particularly when nephron numbers are reduced or other risk factors like hypertension and diabetes are present. A Korean study found an association between higher total protein intake and faster estimated glomerular filtration rate (eGFR) decline. The type of protein is also important. Diets with low carbohydrate and high protein intake could be detrimental to kidney health and may increase the risk of developing CKD. Total and animal proteins are associated with the risk of cardiovascular disease and diabetes, even after adjusting for lifestyle and nutritional factors. Epidemiological studies show that animal-derived proteins and fats, especially from red and processed meats, are risk factors for CKD development. High salt and sugar-sweetened beverage intake are also established risk factors for kidney function decline.
Dietary Acid Load
A high dietary acid load (DAL) can increase the risk of developing chronic kidney disease. High-DAL diets can induce low-grade metabolic acidosis, potentially leading to insulin resistance, diabetes, hypertension, bone disorders, low muscle mass, kidney stones, hyperuricemia, and non-alcoholic hepatic steatosis. Plant-based and vegetarian diets are associated with a reduction in DAL. Vegetarians consume less protein and phosphorus but more magnesium and potassium, resulting in more favorable DAL scores. A controlled trial showed that a vegan diet significantly lowered the potential renal acid load compared to a meat-rich diet. Besides DAL and glomerular hyperfiltration, other potential mediators of kidney damage from animal protein include phosphate content, gut microbiome dysbiosis, and inflammation.
Phosphate
Chronic dietary phosphate excess can lead to higher blood levels, and the homeostatic response (phosphaturia) can increase the risk of kidney function decline. High dietary phosphate intake and hyperphosphatemia are risk factors for kidney function decline and are associated with increased cardiovascular disease and mortality risk in the general population. Plant-based diets, which provide phosphate in less bioavailable forms, and avoidance of processed foods containing inorganic phosphate food additives can reduce dietary phosphate absorption.
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Gut Microbiome
A westernized diet high in fat and low in fiber is associated with worse intestinal health, including impaired intestinal barrier function, leading to leaky gut and low-grade systemic inflammation, which can induce or exacerbate systemic diseases, including kidney dysfunction. Consumption of fresh fruit, whole grains, low-fat dairy products, and vegetable proteins like legumes, soy, and oilseeds appear to be protective against kidney disease.
Observational Studies
In patients with chronic kidney disease, several observational studies have shown that high adherence to healthy dietary patterns rich in plant foods and fibers is associated with a delay in CKD progression and improved survival. Diets with a higher proportion of proteins from plant sources are associated with lower mortality and slower decline in kidney function.
Amino Acids
Amino acid intake is also correlated with the risk of developing CKD. Higher intakes of L-arginine from animal sources and higher loads of branched-chain, alcoholic, and aromatic AAs (predominantly in animal foods) were found to be negative factors for kidney health. Conversely, there was no significant association between total or plant-derived L-arginine intake and the risk of CKD, while higher intakes of acidic AAs, proline, and lower intakes of alkaline AAs and small AAs were related to a decreased risk of CKD.
Vegetarian Diet and Renal Filtration
A systematic review of randomized controlled trials suggests that a vegetarian diet improves renal filtration function in CKD patients.
Advantages of Whole Food, Plant-Based Diets
Whole food, plant-based diets offer two advantages for prevention and treatment of CKD. Dietary patterns focusing on whole plant-based foods may be pivotal in managing chronic kidney disease (CKD). Consuming plant protein over animal protein treats and prevents CKD, and the fiber in plant foods allows for a shift away from the production of uremic toxins and other nitrogenous wastes. The lower protein level of a plant-based diet has favorable effects on secondary hyperparathyroidism, peripheral insulin resistance, hyperlipidemia, hypertension, and acid-base disorders. Plant anions may mitigate metabolic acidosis to slow CKD progression. Animal foods do not contain fiber. Fiber aids in creating and maintaining a healthy microbiome to address toxins, as well as producing anti-inflammatory compounds and reducing the production of uremic toxins.
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Mechanisms of Action
Several underlying mechanisms play a role in kidney dysfunction and CKD progression.
Metabolic Acidosis
The inability of the kidneys to excrete the daily dietary acid load can lead to metabolic acidosis, increasing the risks of hypertension, heart failure, muscle wasting, bone loss, chronic inflammation, progression of renal failure, and death.
Protein Quality
High-protein diets may worsen kidney function in individuals with kidney disease due to the bodyâs demand to eliminate the excess waste products of protein metabolism. Some CKD patient guidelines emphasize protein from animal sources due to their âhigh valueâ to assure that essential amino acids are not limited, but this measurement is based on animal studies and considered outdated. Plant-based proteins contain all essential amino acids and offer the benefits of the fiber and isoflavones present. Dietary interventions can be particularly effective in controlling protein intake.
Trimethylamine N-oxide (TMAO)
Higher risk from animal proteins is likely due to the acidic quality of meat, and the creation of more metabolites in the gut and their effective excretion, particularly trimethylamine N-oxide (TMAO). TMAO is the byproduct of the breakdown of the amino acid carnitine in meat associated with an increased risk of heart disease. High circulating levels of TMAO are linked with increased risk for chronic kidney disease and kidney fibrosis development.
Dietary Acid Load and Alkaline Foods
The primary source of acid production in the body can be traced to diet. Acid in the diet comes primarily from protein which releases sulfuric acid when metabolized. The Western diet favoring animal protein made of sulfur-based amino acids promotes an acidic environment in the body. In contrast, plant foods are alkaline, which protects against dietary acid load.
Hyperphosphatemia
Hyperphosphataemia is a condition of excess phosphorus levels in the blood, commonly caused by kidney failure. Polysaccharides found in plant foods contain dietary fiber to decrease toxins and facilitate the excretion of nitrogen.
Gut Microbiota and Uremic Toxins
Fiber intake increases intestinal motility as well as fecal excretion. It allows the gut microbiota to build numerous beneficial colonies of bacteria and reduce uremic toxin production. Despite evidence demonstrating the benefits of plant-based diets containing fiber, most CKD patients consume well below recommendations (25 g/day for women and 38 g/day for men). Gut microbiota breaks down and ferments animal protein, which produces toxins normally cleared by the kidneys. Excessive animal food in the diet of CKD patients leads to alteration of the colonic environment in microbial dysbiosis and disturbances in the intestinal mucosa barrier.
Potassium
Although there is a concern about hyperkalemia in CKD patients, recent case studies indicate that lack of fiber from whole foods may be the ameliorating factor. Feeding trials in healthy people suggest that potassium recovery from animal-based diets is about 80% and 50â60% from plant-based diets. Animal-based protein induces hyperfiltration, which temporarily overworks the kidneys, while an equivalent amount of plant protein does not induce the same stress.
Potassium Absorption
Fruits and vegetables are naturally rich in potassium which is readily absorbable by the proximal intestine. However, absorption may be influenced by alkaline load. Since the metabolic breakdown of proteins increases acidity, meat and cheese have the highest potential for renal acid load, whereas fruits and vegetables have the lowest. Also, dietary recall may underestimate potassium consumption by failing to account for the cooking loss. Soaking, freezing, or boiling leads to a 60â90% potassium loss of several raw foods and introduces inaccuracy by not accounting for this differential bioavailability. Sauces and juices lack fiber, which uniquely increases potassium consumption compared to whole food form. Plant foods with low potassium content, such as apples, berries, cabbage cauliflower, eggplant, and squash, are a good choice for those who need to restrict potassium.
Dialysis Patients
There is a paucity of evidence evaluating the potential benefits of plant-based diets in patients undergoing dialysis. Traditionally, patients on dialysis are discouraged from adopting plant-based diets mainly due to two perceived risks: inadequate protein intake and hyperkalemia, yet general population studies show that the risk of nutritional deficiencies from plant-based diets is low.
Phosphorous Absorption
Though phosphorous is in plant foods, it is not absorbed efficiently. Animal protein is the primary source of bioavailable phosphorus. Phosphorous in plant foods is primarily bound to phytate, which is poorly absorbed since humans lack the enzyme phytase to break it down.
Acid-Base Homeostasis
The kidneys regulate acid-base homeostasis, and acid-load is primarily modulated by diet. A higher acid load accelerates kidney damage and eGFR decline, whereas an alkaline diet reverses these processes. Compared with animal-based diets, plant-based diets have a lower non-volatile acid load, as they are richer in organic anions than cations. Additionally, the increased fiber intake found in plant foods allows the gut microbiota to generate more short-chain fatty acids, which are alkali.
Clinical Markers and Outcomes
Multiple studies demonstrate favorable associations and clinical markers for CKD between plant-based diets, naturally low in protein. The risk of kidney stones from uric acid crystallization decreases with vegetarian diets, as does fibroblast growth factor-23 (FGF23). Both phosphorous excretion and accumulation show improvement, as do glomerular filtration rate (eGFR), renal plasma flow (RPF), and albuminuria; thus, mortality rates are better as well.
Case Studies
A recent case study demonstrates the ability of a strict whole food, plant-based diet to restore health for a 69-year-old male with type 2 diabetes, hypertension, and stage 3 CKD. Another case details a 57-year-old woman with essential hypertension, obesity, type 2 diabetes, hyperlipidemia, and CKD, a set of comorbidities that is not uncommon in the US.
Considerations for Elderly Patients
A plant-based dietary approach with its high nutritional value and lower protein values may resolve issues of compliance with restrictive âtraditionalâ low-protein diets in elderly patients with kidney disease. Though protein restriction may retard the need for renal replacement therapy, high protein intake is believed to contribute to preserving nutritional status in elderly patients or in patients with high comorbidity. Studies indicate that the benefits of plant-based diets can be applied to all populations to address kidney dysfunction, even in the elderly at advanced stages.
Plant-Based Diet for Hyperuricemia Patients
Hyperuricemia is a well-known risk factor for chronic kidney disease (CKD). A vegan diet is associated with a 31% lower risk of CKD in patients with hyperuricemia.
Study Design and Results
A cross-sectional study included 3618 patients with hyperuricemia, consisting of 225 vegans, 509 lacto-ovo vegetarians, and 2884 omnivores. After adjusting for age and sex, vegans had a significantly lower odds ratio (OR) of CKD than omnivores (OR, 0.62; p = 0.006). The OR of CKD remained significantly lower in vegans after adjusting for additional confounders (OR, 0.69; p = 0.04).
Risk Factors for CKD
Age (per year OR, 1.06; p < 0.001), diabetes mellitus (OR, 2.12; p < 0.001), hypertension (OR, 1.73; p < 0.001), obesity (OR, 1.24; p = 0.02), smoking (OR, 2.05; p < 0.001), and very high uric acid levels (OR, 2.08; p < 0.001) were independent risk factors for CKD in patients with hyperuricemia.