The goal of this non-commercial clinical trial is to assess efficacy and safety of ketoanalogues of essential amino acids in the prevention of protein-energy wasting in nephrotic syndrome.

Adult patients with new diagnosis or relapse of nephrotic syndrome and glomerular filtration rate of ≥ 30 mL/min/1.73m2 will be included in the study. Exclusion criteria will be a secondary cause of nephrotic syndrome, morbid obesity and severe diseases affecting nutritional status.

Participants will be randomly assigned to the intervention group (KA+MPD) or control group (MPD); randomization will be stratified by type of glomerular disease (podocytopathy or other type) and investigational site. The control group will follow the diet recommended in nephrotic syndrome - a medium protein diet (MPD) - under the care of a dietitian. Intervention group will receive Ketosteril (1 tablet for every 5 kg of ideal body weight) as an addition to the diet. All patients will also receive treatment for underlying glomerular disease in accordance with current guidelines and local practice.

The main objective is to assess the efficacy of Ketosteril as an add-on therapy in preventing the loss of lean tissue mass (LTM) over 6 months compared to a standard diet.

The additional aims include the assessment of muscle function parameters, nephrotic syndrome severity and laboratory indicators of catabolism.

Inclusion Criteria:

• Nephrotic syndrome with serum albumin < 3.0 g/dL and daily proteinuria of > 3.5 g/day or > 50 mg/kg;
• New diagnosis or relapse of nephrotic syndrome (defined as: proteinuria of < 2.0 g/day or uPCR < 2000 mg/g in the last 6 months prior to relapse and prednison dose equal to or less than 10 mg/day in the last 3 months prior relapse);
• Glomerular filtration rate qual to or higher than 30 mL/min/1.73m2 based on Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.

Exclusion Criteria:

• Diabetic kidney disease;
• Small vessels vasculitis;
• Systemic lupus erythematosus;
• Positive antinuclear antibodies, anti-dsDNA or antineutrophil cytoplasmic antibodies (ANCA);
• Positive anti-HIV or anti-hepatitis C antibodies, HBsAg;
• HbA1c >7%;
• Monoclonal gammopathy;
• Pregnancy;
• Body mass index >= 40 kg/m2;
• Severe acute or chronic disease affecting nutritional status;
• Neoplasm;
• Contraindication to Ketosteril;
• Alcohol or drug abuse;
• Mental disorders;
• Failure to comply with medical recommendations, lack of cooperation;
• Participation in other clinical trial or the use of Ketosteril in the last 1 year prior to screening.