Effects of Minimally vs. Ultra-Processed Diets on Potassium (K) Handling in CKD

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 and stool 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.


Eligibility Criteria:
Inclusion Criteria:

* Adults (≥18 years) with stage 3B-5 CKD not on dialysis.
* Stable baseline serum potassium (≤5.5 mmol/L, ≤3 episodes of hyperkalemia in the past year)
* Able and willing to follow a controlled feeding regimen, attend in-person visits, provide informed consent, and comply with study procedures.

Exclusion Criteria:

* Genetic or other unique health conditions affecting potassium handling.
* Foreseen start of renal replacement therapy (RRT) within the next 6 months.
* Anticipated renal replacement therapy (RRT) or preemptive kidney transplant within 6 months.
* Acute Kidney Injury (AKI) within 3 months.
* Kidney Failure Risk Equation (KFRE) \> 40% within 2 years.
* History of kidney transplant.
* Active glomerulonephritis.
* Acute myocardial infarction (AMI) or stroke within 6 months.
* Active cancer, autoimmune disease, or inflammatory bowel disease (IBD).
* Ileostomy or short bowel syndrome.
* Body mass index (BMI) \<18.5 or ≥35.
* NYHA Class 3 or 4 congestive heart failure (CHF).
* History of ventricular arrhythmia.
* Recent admission to an intensive care unit (ICU), major surgery, or poorly controlled diabetes (HbA1c \>10%) in past 3 months.
* Gastroparesis.
* Chronic nausea and vomiting.
* Significant psychiatric disease.
* Uncontrolled blood pressure (above 160/100)
* Use of immunossupressives, potassium binders, lithium, motility agents, \>2 medications that inhibit renal potassium excretion, or supplements known to influence potassium levels.
* Fluid volume status or hypertension under active management.
* Reliance on tube feeding or total parenteral nutrition (TPN).
* Non-adherence to prescribed medications or therapeutic measures.
* Pregnancy or lactation.
* Strict dietary preferences (e.g., vegetarians, vegans) or allergies/intolerance that preclude participation in diet phases.
* Transitioning transgender.