Introduction
Chronic Kidney Disease (CKD) is a significant global health concern, affecting millions worldwide. As the prevalence of CKD continues to rise, researchers are exploring various dietary interventions to manage its progression and associated complications. Vegetarian and vegan diets have gained popularity due to their potential health benefits, particularly in cardiovascular health. This article delves into the existing research on the effects of vegan diets on kidney function in CKD patients, providing a structured overview of the current understanding.
Understanding Vegetarian and Vegan Diets
Vegetarian diets encompass a range of eating patterns, with the most common being the lacto-ovo vegetarian diet, which includes fruits, vegetables, dairy products (milk, cheese), eggs, and honey. Pescetarianism is another variation that incorporates fish. In contrast, a vegan diet strictly excludes all animal products, allowing only the consumption of fruits and vegetables.
The increasing popularity of vegetarian and vegan diets stems from their association with lower levels of common risk factors, such as BMI, fasting glucose, LDL-cholesterol, and triglycerides. Studies have shown that dietary changes, especially with vegan diets, can significantly reduce total cholesterol and LDL-cholesterol levels. Moreover, vegetarians and vegans often exhibit lower systolic and diastolic blood pressure compared to meat-eaters, along with improved insulin sensitivity. Plant-based diets also promote phosphorus homeostasis, which is beneficial for CKD patients.
Methodology and Materials
This review follows the PRISMA 2020 Checklist and PRISMA 2020 flow diagram to ensure a systematic and transparent approach. The research strategy involved searching databases like PubMed and Cochrane using terms such as ‘vegetarian diet’ AND ‘nephropathy’, ‘eGFR’, ‘albuminuria’, ‘chronic kidney disease’. The search included randomized controlled trials and non-randomized controlled trials published in English, without any year restrictions due to the limited number of studies available.
Inclusion Criteria
The inclusion criteria were based on the PICO elements:
Read also: Managing Stage 3 Kidney Disease with Diet
- Population (P): CKD patients
- Intervention (I): Plant-based diets (vegetarian and vegan)
- Comparison (C): Standard omnivore diet
- Outcomes (O): Changes in estimated glomerular filtration rate (eGFR)
Studies with a duration shorter than 4 weeks or those published in languages other than English were excluded. Two researchers independently selected and reviewed the studies, resolving any discrepancies through discussion. A data extraction tool was used to gather information on diet type, study duration, year, group size, initial and final eGFR, and p-values.
Data Collection Process
The initial search yielded 33 records from Cochrane and PubMed, which were reduced to 22 after removing duplicates. After screening, 16 records were excluded due to inadequate or missing data. The remaining six full papers were assessed, and four RCTs met the inclusion criteria.
Studies that did not meet the inclusion criteria were excluded. One study comparing the effects of meat and meat-free meals was excluded due to its short duration. Another study comparing vegetarian and omnivore diets in terms of protein source and phosphate homeostasis was excluded because it did not measure final eGFR and had a short duration of 7 days.
Risk of Bias Assessment
The risk of bias was assessed using the RoB 2 tool for each study. Two researchers independently evaluated the studies, and any discrepancies were resolved through discussion. The bias assessment considered factors such as randomization, allocation concealment, blinding of data assessors, missing data, and data analysis methods. The results of the bias assessment are presented as a forest plot, which helps determine the validity of the data collected from the included studies.
Results: Impact of Vegan Diets on Kidney Function
The systematic review included four RCTs with a total of 346 participants. Two studies reported a significant positive impact of a vegetarian diet on eGFR, while the other two found no significant differences between the experimental and control groups.
Read also: A Review of the Mediterranean Diet in Kidney Disease
- Dinu et al. and Garneata et al. found a significant positive impact of a vegetarian diet on eGFR in the experimental group (p = 0.001 and p = 0.01, respectively).
- Two studies reported no significant difference in eGFR between the experimental and control groups.
A significant difference was observed between a lacto-ovo-vegetarian diet and the Mediterranean diet, with a mean difference of 4.2 mL/min/1.73 m² (p < 0.001) in the final eGFR. There was an increase of 3.4 mL/min/1.73 m² between the initial and final eGFR in the vegetarian diet group, indicating a positive impact on eGFR.
In a study involving a ketoanalogue-supplemented vegetarian very low protein diet (KD), a significant difference was found between the two diet types. A mean difference was observed between the final eGFR of 4.3 mL/min/1.73 m² (p < 0.01) of KD and a conventional low protein diet (LPD). Furthermore, a decrease of 2.9 mL/min/1.73 m² was reported in KD. However, it is crucial to note that the reduction in eGFR was lower in KD compared to the decrease in LPD (7.1 mL/min/1.73 m²). The other two studies presented no significant differences in the final eGFR between the study groups, thus, the changes between the groups were not analyzed
Other Renal Parameters
In one study, a significant difference was found (p = 0.001) in creatinine level between a vegetarian group (0.72 g/dL) and the Mediterranean diet group (0.76 g/dL). Additionally, at the end of the study, there was a considerable change in the serum urea concentration between the groups consuming a ketoanalogue-supplemented vegetarian very low-protein diet (KD) - 120 mg/dL, and a low-protein diet (LPD) - 226 mg/dL. Moreover, the rate of urinary albumin exertion (UAER) was visibly lower in the LPD group (229.3ug/min) in comparison to the UD (312.8ug/min) and CD (269.4ug/min) (P < 0.001). A significant reduction in serum phosphates was found in favor of the KD group 4.4 mg/dl (4.3-4.5) vs. LPD 6.2 mg/dl (5.8-6.5).
Bias Assessment Analysis
The systematic review included two randomized cross-over trials and two randomized parallel-group trials. The risk of bias assessment of a study by Dinu et al. was estimated using the study protocol. This study demonstrated a low risk of bias in all domains of ROB2 tool. Another study presenting low risk of overall bias was conducted by Garneata et al. In fact, it was the largest study included in the review.
The study performed by de Mello et al. in 2006 presented an overall high risk of bias. Another crossover randomized trial by Soroka et al. in 1998 also presented a high risk of biased.
Read also: Nutrition and stage 2 CKD
Discussion: Benefits of Plant-Based Diets in CKD Management
The findings from the included studies suggest that a vegetarian diet may improve renal filtration function in CKD patients. Plant-based diets are associated with a lower risk of hypertension, diabetes, cardiovascular disease, and mortality. In healthy individuals, observational studies found that greater intake of plant protein and higher adherence to plant-based diets was associated with a lower risk of CKD. In those with CKD, plant-based diets were associated with a lower risk of mortality, improved kidney function, and favorable metabolic profiles.
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.
Addressing Concerns and Ensuring Nutritional Adequacy
Despite the potential benefits, there are concerns about the use of plant-based diets in CKD patients, including nutritional deficiencies and hyperkalemia risk.
- Protein Quality: Plant-based proteins contain all essential amino acids and offer the benefits of fiber and isoflavones.
- Dietary Acid Load: Plant foods are alkaline, which protects against dietary acid load.
- Hyperphosphatemia: Phosphorous in plant foods is primarily bound to phytate, which is poorly absorbed since humans lack the enzyme phytase to break it down.
- Hyperkalemia: Though plant foods generally contain more potassium than animal foods, the accompanying fiber decreases potassium absorption and helps to avoid hyperkalemia by facilitating the excretion of potassium.
The Role of Fiber and Gut Microbiota
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. 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.
Plant-Based Diets in Dialysis Patients
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.
Recent Studies and Findings
A recent study published in the National Kidney Foundation American Journal of Kidney Diseases (AJKD) provided new insights into the role of diet in the management of chronic kidney disease (CKD). The study revealed that adhering to an overall plant-based diet and a healthy plant-based diet is associated with a reduced risk of all-cause mortality among CKD patients. Conversely, those following an unhealthy plant-based diet face an elevated risk of CKD progression and all-cause mortality.
Key findings of the study include:
- Participants with the highest adherence to overall plant-based diets and healthy plant-based diets had a 26% and 21% lower risk of all-cause mortality, respectively.
- Each 10-point higher score on the unhealthy plant-based diet index was associated with a 14% and 11% higher risk of CKD progression and all-cause mortality, respectively.
Importance of Dietary Quality
This study emphasizes the importance of dietary quality by distinguishing between overall plant-based diets, healthy plant-based diets, and unhealthy plant-based diets. Healthier plant-derived foods include whole fruits and vegetables, whereas unhealthy plant-derived foods include things like sugar-sweetened beverages.
Practical Implications and Dietary Recommendations
For individuals with early kidney disease, a plant-based diet can offer several benefits:
- Healthy Weight Management: Plant-based foods usually have fewer calories than animal-based foods.
- Lower Blood Pressure and Cholesterol: This helps reduce the risk for heart disease, a common complication of kidney disease.
- Reduced Diabetes Risk: Plant-based foods improve insulin sensitivity and help keep blood sugar in check.
- Improved Antioxidant Levels: Abundant in plant-based foods, antioxidants protect cells from damage.
- Slowing Kidney Disease Progression: By lowering the risk of heart disease, diabetes, “bad” cholesterol, and weight gain, a plant-based diet can help slow or stop kidney disease from getting worse.
Dietary Guidelines
To make a plant-based diet as healthy as possible, it's important to:
- Eat mostly whole grains, fruits, vegetables, legumes (beans, peas, and lentils), unsalted nuts, and healthy oils.
- Reduce animal foods such as dairy, eggs, fish, meat, and poultry.
- Avoid processed foods like canned foods and soups, refined grains (white breads and pasta, highly processed or high sugar cereals, white rice), snack-foods (potato chips, cookies), and sugar-sweetened beverages.
Consulting a Dietitian
Given the potential risks and benefits, it is crucial for CKD patients to consult with a registered dietitian or healthcare team before making significant dietary changes. A dietitian can help create a personalized meal plan that meets the individual's nutritional needs while addressing specific concerns related to kidney function and overall health.