The Quest for an Optimal Diet for CKD Patients

Core Message

There is no single "optimal" diet yet established for patients with chronic kidney disease (CKD) or kidney transplant recipients (KTRs). Current dietary guidelines often lean towards being overly cautious or lack sufficient individualization. Objective, mechanistically relevant biomarkers—especially those derived from 24-hour urine collections—should guide nutritional assessments and dietary recommendations.

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Key Themes & Findings

1. The Problem with Traditional Dietary Assessment

Dietary questionnaires are common, but they have significant limitations. Patients frequently under-report or over-report dietary habits based on factors such as social desirability, past exposure to dietary counseling, and misjudgments about portion sizes. These tools particularly struggle to accurately assess critical nutrients like sodium, alcohol, fiber, and protein, all of which are vital in managing kidney disease.

2. Why 24-Hour Urine Biomarkers Matter

Using objective urine biomarkers offers a more reliable method to evaluate dietary intake. Key measurements include:

• Sodium, urea, iodine: Intake closely approximates excretion.

• Potassium, magnesium, cotinine, ethylglucuronide: Levels of absorption can be measured against excretion rates.

• Creatinine excretion: This reflects muscle mass.

  
  

Creatinine excretion acts as a surrogate for muscle mass, which is a crucial predictor of survival and health status in CKD, diabetes, and heart failure. Low muscle mass, indicated by reduced creatinine excretion, correlates with:

• Increased mortality risk

• Higher chances of hospitalization

• Frailty and negative prognoses

  
  

3. The Critical Role of Muscle Mass

Muscle mass plays a vital role in the survival of CKD and kidney transplant patients. Unfortunately, many individuals diagnosed with CKD are at high risk for muscle wasting due to:

• Inflammation

• Malnutrition

• Physical inactivity

• Amino acid loss during dialysis

  
  

Important Note: Weight increases due to fat mass can obscure the simultaneous decrease in muscle mass. This concern is particularly pronounced in CKD patients who may be advised to consume excessive amounts of fluid (for instance, those being treated with Tolvaptan for ADPKD), which could suppress their appetite and protein intake, thereby exacerbating muscle loss.

4. Protein Type Matters

The type of protein consumed is significant.

• Animal proteins are effective in preserving muscle mass and supplying crucial nutrients such as:

• Taurine

• Creatine

• Niacin

• Iodine

• Processed meats are linked to adverse health effects and should be limited.

• Unprocessed meats appear safer and possibly advantageous for health.

  
  

Current guidelines advocating for plant-based diets and low protein intake may require reevaluation, particularly for patients facing malnutrition or muscle loss.

5. Nutrient Loss During Dialysis

Dialysis removes waste products but also depletes vital nutrients, including:

• Amino acids

• Creatine

• Vitamin C

• Niacin

  
  

These losses are often understudied but could have significant implications for nutritional health and long-term outcomes.

6. Vitamins at Risk: Niacin and Vitamin C

• Niacin (Vitamin B3) is essential for energy metabolism and cellular repair. Primary sources include meat, fish, and green vegetables, yet it is frequently overlooked among CKD patients.

• Vitamin C metabolism changes in CKD. Contrary to assumptions, its levels may not increase despite decreased excretion due to reactions with benzoic acid (from diet or gut metabolism) that forms benzene, a toxin. Detoxifying benzoic acid requires glycine and healthy kidneys to create hippuric acid, an impaired process in CKD. This raises toxicity risks.

  
  

Concern: High consumption of ultra-processed foods and additives (including sodium benzoate) may aggravate this issue.

7. Ultra-Processed Foods (UPFs) and Sugary Beverages

High intake of UPFs is associated with:

• Increased mortality risk among kidney transplant patients

• Deterioration of body composition: More fat, less muscle

  
  

Patients advised to drink ample fluids (e.g., ADPKD patients on Tolvaptan) often choose sugary drinks, further complicating health outcomes. Water should always be the preferred option.

8. Heat Stress, Dehydration & Kidney Injury

Another factor that is often overlooked is the impact of environmental heat and repeated dehydration.

• Research involving manual laborers (e.g., sugarcane workers) indicates that extreme heat, coupled with NSAID use, can lead to chronic kidney damage.

  
  

The kidney's proximal tubule is particularly susceptible to repeated ischemia (lack of blood flow).

Mechanism: Recurring dehydration increases serum osmolarity, which activates the polyol pathway within the kidney, leading to:

• Glucose → Sorbitol → Fructose

• Fructose metabolism (via fructokinase) contributes to:

- Uric acid

- Oxidative stress

- Inflammation

In animal studies, fructokinase-deficient mice displayed protection against dehydration-induced kidney damage.

9. Plant-Based vs. Animal-Based Diets

• Vegetables (more than fruits) seem protective, likely due to their lower fructose content and lesser impact on serum vitamin C interactions.

• Plant-based diets might minimize UPF intake but often lack:

• Creatine

• Taurine

• Bioavailable iron

  
  

An emphasis on balanced, context-specific diets may provide better outcomes than strict adherence to dietary ideologies such as low protein or solely plant-based diets.

Conclusions

• Western-style, heavily processed diets pose risks to CKD and transplant patients.

• Animal-based nutrition (especially unprocessed meat) might be underutilized.

• 24-hour urinary biomarkers offer personalized, data-driven insights into dietary needs.

• Preservation of muscle mass should receive greater clinical focus.

• Consideration of nutrient losses from dialysis and the metabolic impacts of dehydration should be prioritized in future research.

  
  

Final Reflection

Professor Bakker emphasized that we still lack a definitive "optimal diet." For CKD and kidney transplant patients, rather than imposed blanket recommendations, we need:

• Individualized plans based on objective biomarkers

• A focus on the importance of muscle mass preservation

• Recognition of environmental and lifestyle risk factors

• A paradigm shift from dogma to data

  
  

In CKD, nutrition should be regarded as more than just avoiding harm—it should prioritize actively preserving function and health.

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❓ FAQ: Diet and Nutrition for CKD and Kidney Transplant Patients

Q1: Is there one optimal diet for all CKD and kidney transplant patients?

A: No. According to Prof. Stephan Bakker, there is no single “optimal” diet. Nutrition should be personalized based on individual health status, medications, and biomarker data like 24-hour urine collections.

Q2: How important is protein in a kidney-friendly diet?

A: Protein intake is critical, especially to preserve muscle mass. While guidelines often recommend low-protein diets, patients at risk of malnutrition may benefit from higher-quality animal proteins—especially unprocessed meats.

Q3: What is the role of 24-hour urine tests in nutrition planning?

A: These tests provide objective data on nutrient intake and muscle mass. For example, creatinine excretion can indicate muscle mass, which is a strong predictor of survival in CKD and transplant patients.

Q4: Are plant-based diets better for kidney disease?

A: No. While plant-based diets can reduce ultra-processed food intake, they may lack key nutrients like creatine, taurine, and bioavailable iron. A balanced approach is usually better than strict plant-only ideology.

Q5: Can sugary drinks or processed foods harm kidney patients?

A: Yes. Ultra-processed foods (UPFs) and sugary beverages are linked to higher mortality and poorer muscle-to-fat ratios in kidney transplant patients. Water should be the preferred fluid, especially for those on medications like Tolvaptan.

Q6: Why is muscle mass so important for CKD patients?

A: Low muscle mass is associated with higher mortality, more hospitalizations, and worse outcomes. CKD and dialysis can cause muscle loss, so nutrition plans should aim to preserve lean body mass.

Q7: Do dialysis patients lose nutrients during treatment?

A: Yes. Dialysis can remove essential nutrients like amino acids, creatine, niacin, and vitamin C. These losses are often overlooked and may require dietary or supplemental strategies to correct.

Q8: What are some hidden risks in vitamin C supplementation?

A: In CKD, vitamin C doesn’t always accumulate as expected. It can interact with dietary benzoates to form benzene, a toxic compound. This is a concern with high intake of food additives found in processed foods.

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About Professor Stephan J.L. Bakker

Prof. Stephan J.L. Bakker is a leading nephrologist and professor of Internal Medicine at the University Medical Center Groningen (UMCG), Netherlands. His clinical and research career spans more than 25 years, with expertise in:

• Chronic Kidney Disease (CKD) and kidney transplantation

• Clinical nutrition and biomarker-based assessment

• Muscle mass and metabolic health in chronic disease

  
  

He leads the Groningen Institute for Organ Transplantation and coordinates the PREVEND cohort study, a population biobank with over 8,500 participants.

Key Contributions to CKD Nutrition Research

• Pioneer of 24-hour urine collection as an objective dietary tool, advocating for its use over self-reported food questionnaires.

• Highlights muscle mass (via urinary creatinine) as a significant biomarker for survival and frailty in CKD, heart failure, and diabetes.

• Warns against ultra-processed foods (UPFs), which his studies indicate increase the risk of CKD progression—even when controlling for macro- and micronutrient intake.

• Supports individualized nutrition, especially for patients undergoing dialysis or taking medications like Tolvaptan, where protein and fluid intake need careful management.

• Emphasizes the value of unprocessed animal protein in preserving muscle mass and providing essential nutrients such as taurine, creatine, and niacin.

  
  

With over 1,500 scientific publications and approximately 60,000 citations, Prof. Bakker is a prominent voice in redefining what an “optimal diet” means for CKD and kidney transplant patients.

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