What is this study about?

This clinical trial is designed to learn how potassium from different types of food affects blood potassium levels and overall health in people with chronic kidney disease (CKD, stages 3B-5).

People with CKD are often advised to avoid potassium-rich foods, even though fresh fruits and vegetables are important for good health. However, potassium in processed foods (such as packaged snacks and ready-made meals) may be absorbed differently than potassium from fresh foods.

This study will compare minimally processed vs. ultra-processed foods to determine how different sources of potassium affect potassium levels and help create better dietary recommendations for people with CKD.

What are the study goals?

The study will answer:

• Does potassium from fresh foods (like fruits and vegetables) affect blood potassium differently than potassium from processed foods?
• How does dietary potassium impact potassium absorption and excretion in people with CKD?

Researchers will compare the effects of four diets to understand how low and normal-potassium rich diets from fresh vs. processed foods influence:

• Blood potassium levels
• Body composition (muscle, fat, and fluid balance)
• Vascular health

What will participants do?

Participants will follow four different 10-day diets over the course of the study. All food will be provided at no cost. These diets are:

• Minimally processed with low-potassium content
• Minimally processed with normal potassium content
• Ultra-processed with with low-potassium content
• Ultra-processed with normal potassium content

There will be 16-day breaks (washout period) between diets where participants return to their normal eating habits.

During the study, participants will:

• Pick up prepared meals from the research center approximately 3 times per week.
• Attend checkups for weight, blood pressure, and blood tests.
• Provide urine samples to track potassium levels.
• Wear a comfortable, cuff-free blood pressure monitor at home.
• Keep a study journal to track diet, medications, and symptoms.
• Complete questionnaires about diet satisfaction and health changes.

Inclusion Criteria:

• Participants aged ≥18 years living with stage 3B-5 CKD (estimated glomerular filtration rate ≥ 15 mL/min/1.73m2) on conservative kidney management (not on dialysis).
• Able and willing to follow a controlled feeding regimen, attend in-person visits, provide informed consent, and comply with study procedures.

Exclusion Criteria:

General

• Pregnant or lactating women.
• Transitioning transgender individuals.
• Individuals with strict dietary preferences (e.g., vegetarians, vegans) or allergies/intolerance that would preclude participation in the diet phases.

Kidney Function

• Foreseen start of renal replacement therapy within the next 6 months.
• Acute kidney injury in the past 3 months.
• 2-year Kidney Failure Risk Equation > 40%.
• Preemptive kidney transplant planned within the next 6 months.
• History of kidney transplant.
• Active glomerulonephritis. Comorbidities
• Acute myocardial infarction or stroke within the past 6 months.
• Active cancer.
• Ileostomy, short bowel syndrome or inflammatory bowel disease.
• Body mass index < 18.5 or ≥ 35.
• New York Heart Association Class III or IV congestive heart failure.
• History of ventricular arrhythmia.
• Major surgery within the past 3 months.
• Active autoimmune disease.
• Glycated hemoglobin > 10% within the past 3 months.
• Gastroparesis.
• Chronic nausea and vomiting.
• Intensive care unit admission within the past 3 months.
• Significant psychiatric disease.
• Uncontrolled blood pressure (above 160/100). Current Use of Medications/Supplements
• Immunosuppressives.
• Potassium binders.
• Lithium.
• Motility agents.
• More than 2 medications that inhibit renal potassium excretion (e.g., angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, mineralocorticoid receptor antagonists).
• Supplements known to influence potassium levels. Potassium-Related Conditions
• Potassium > 5.5 mmol/L in more than 3 episodes within the past year.
• Participants with genetic issues affecting potassium handling (e.g. Barter and Liddle syndrome) or other unique health conditions that could interfere with potassium handling.

Intervention-related Conditions

• Fluid volume status or hypertension being actively managed. Other Factors
• Documented non-adherence to medications or other therapeutic measures.
• Use of tube feeding or parenteral nutrition.

We have not yet finalized a plan for sharing individual participant data. The decision will depend on several factors, including participant consent, ethical approval, and institutional policies regarding data privacy and security. Future data sharing may be considered upon additional ethical review and participant consent.