What Is the Optimal Diet for CKD and Kidney Transplant Patients?

A summary of Professor Stephan Bakker’s presentation at ERA25 (Vienna, June 2025)

Infographic: Optimal DIet for CKD

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 are often overly cautious or not sufficiently individualized. Objective, mechanistically relevant biomarkers—especially from 24-hour urine collections—should guide nutritional assessment and dietary recommendations.

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Key Themes & Findings

1. The Problem with Traditional Dietary Assessment

Dietary questionnaires are widely used but prone to serious limitations. Patients often under-report or over-report based on:

• Social desirability

• Previous exposure to diet counseling

• Misjudging portion sizes

These methods are particularly poor at estimating sodium, alcohol, fiber, and protein intake—nutrients crucial in kidney disease management.

2. Why 24-Hour Urine Biomarkers Matter

Objective urine biomarkers provide a far more reliable way to assess diet:

• Sodium, urea, iodine: Intake ≈ excretion

• Potassium, magnesium, cotinine, ethylglucuronide: Absorption ≈ excretion

• Creatinine excretion: Reflects muscle mass

Creatinine excretion serves as a surrogate for muscle mass, a powerful predictor of survival and health status in CKD, diabetes, and heart failure. Low muscle mass (reflected by low creatinine excretion) signals:

• Increased mortality risk

• Higher hospitalization risk

• Frailty and poor prognosis

3. The Critical Role of Muscle Mass

Muscle mass is a key survival factor in CKD and kidney transplant patients. Yet, many CKD patients are at high risk of muscle wasting due to:

• Inflammation

• Malnutrition

• Physical inactivity

• Dialysis-related amino acid loss

Important note: An increase in body weight due to fat mass can mask a simultaneous loss of muscle mass. This is especially concerning in CKD, where patients may be encouraged to consume large amounts of fluid (e.g., in Tolvaptan-treated ADPKD), potentially suppressing appetite and protein intake—worsening muscle loss.

4. Protein Type Matters

• Animal proteins may better preserve muscle mass and supply critical nutrients like:

  • Taurine

  • Creatine

  • Niacin

  • Iodine

• Processed meat is associated with negative health outcomes and should be limited.

• Unprocessed meat appears safer and potentially beneficial.

Current guidelines promoting plant-based diets and low protein intake may need reevaluation, especially for patients at risk of malnutrition or muscle loss.

5. Nutrient Loss During Dialysis

Dialysis doesn't just remove waste—it also depletes essential nutrients, including:

• Amino acids

• Creatine

• Vitamin C

• Niacin

These losses are poorly studied but may have major consequences for nutritional status and long-term outcomes.

6. Vitamins at Risk: Niacin and Vitamin C

• Niacin (Vitamin B3) is essential for energy metabolism and cellular repair.

  Sources: Meat, fish, green vegetables

  Risk: Often overlooked in CKD patients.

  
  

• Vitamin C metabolism is altered in CKD. Contrary to assumptions, levels may not rise despite reduced excretion.

  A possible reason: Vitamin C reacts with benzoic acid (from diet or gut metabolism), forming benzene, a known toxin. Benzoic acid detox requires glycine and functioning kidneys to form hippuric acid. In CKD, this process is impaired, raising toxicity risks.

Concern: High intake of ultra-processed foods and additives (like sodium benzoate) could worsen this issue.

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

High UPF intake is associated with:

• Increased mortality risk in kidney transplant patients

• Poorer body composition: Increased fat, decreased muscle

Patients advised to drink large amounts of fluid (e.g., ADPKD on Tolvaptan) often consume sugary beverages, worsening outcomes.Water should always be the fluid of choice.

8. Heat Stress, Dehydration & Kidney Injury

One often overlooked factor: environmental heat and recurrent dehydration.

• Studies of manual laborers (e.g., sugarcane workers) show that working in extreme heat, combined with NSAID use, contributes to chronic kidney damage.

• The kidney’s proximal tubule is especially vulnerable to repeated ischemia (lack of blood flow).

Mechanism:Recurrent dehydration raises serum osmolarity, activating the polyol pathway in the kidney. This leads to:

• Glucose → Sorbitol → Fructose

• Fructose metabolism (via fructokinase) triggers:

  • Uric acid

  • Oxidative stress

  • Inflammation

In animal studies, fructokinase-deficient mice were protected from dehydration-induced kidney injury.

9. Plant-Based vs. Animal-Based Diets

• Vegetables (more than fruits) appear protective, possibly due to lower fructose content and less impact on serum vitamin C interactions.

• Plant-based diets help reduce UPF intake but may lack:

  • Creatine

  • Taurine

  • Bioavailable iron

• Balanced, context-specific diets are likely superior to rigid dietary ideologies, such as low protein, plant based diets.

Conclusions

• Western-style, highly processed diets are harmful to CKD and transplant patients.

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

• 24-hour urinary biomarkers offer personalized, data-driven dietary insight.

• Muscle mass preservation is vital and deserves more clinical attention.

• Nutrient losses from dialysis and metabolic effects of dehydration are urgent research areas.

Final Reflection

Professor Bakker emphasized that we still lack a definitive "optimal diet" for CKD and kidney transplant patients. Instead of blanket recommendations, we need:

• Individualized plans based on objective biomarkers

• Focus on muscle mass preservation

• Awareness of environmental and lifestyle risk factors

• A shift from dogma to data

In CKD, nutrition is not just about avoiding damage—it's about 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?

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

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 powerful biomarker for survival and frailty in CKD, heart failure, and diabetes.

• Warns against ultra-processed foods (UPFs), which his studies show 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 attention.

• Emphasizes the value of unprocessed animal protein in preserving muscle mass and providing essential nutrients like 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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