This clinical investigation is designed to evaluate the potential therapeutic effects of kefir peptides as an adjunct intervention for chronic kidney disease (CKD) and clinical proteinuria. Patients diagnosed with stage 3 or 4 CKD will receive a three-month course of kefir peptide supplementation. Throughout the intervention period, the investigator will monitor renal function markers (blood urea nitrogen, serum creatinine), proteinuria (urine protein-to-creatinine ratio), inflammatory indicators (high-sensitivity C-reactive protein), and additional biochemical parameters relevant to CKD progression.

Background and Aim Chronic kidney disease (CKD) represents a substantial global public health burden, with prevalence rising due to population aging and an increased incidence of systemic conditions such as hypertension, diabetes mellitus, metabolic syndrome, and chronic exposure to nephrotoxic agents. Accumulation of uremic toxins in CKD contributes to gut dysbiosis, systemic inflammation, accelerated renal functional decline, and heightened cardiovascular risk.

Probiotics and postbiotics have been evaluated as potential adjunct therapies to slow CKD progression; however, conclusive evidence supporting their clinical effectiveness remains limited. Kefir peptides (KPs) contain bioactive constituents with documented antioxidant, antidiabetic, antithrombotic, antibacterial, anti-osteoporotic, and immunomodulatory properties. Based on these characteristics, KPs may offer therapeutic benefits in modulating renal function, systemic inflammation, and uremic toxin burden in individuals with advanced CKD.

The current investigation aims to examine the effects of kefir peptides on renal function and clinical proteinuria, and to explore possible mechanistic pathways contributing to these outcomes.

Methods A total of 165 participants were enrolled: 83 in the placebo group and 82 in the kefir peptide group. All participants consumed the assigned kefir formulation twice daily for three months. Blood and urine biochemical assessments were conducted at baseline (week 0), week 4, and week 12. Serum high-sensitivity C-reactive protein (hs-CRP), indoxyl sulfate (IS), and p-cresyl sulfate (PCS) levels were measured at baseline and at week 12. All study procedures and monitoring activities were performed by the investigator.

Inclusion Criteria:

• Age: 30-82 years of age
• Chronic kidney disease stage 3 and 4
• Sign informed consent

Exclusion Criteria:

• Acute illness
• Pregnancy
• Aboriginal descent

Individual participant data (IPD) will not be shared due to concerns regarding patient privacy and confidentiality. Only de-identified and aggregated data will be included in future publications or presentations.

Participants and investigators were unaware of group assignment; placebo was identical in appearance to study