Supplemented Low Protein Diet and Progression of CKD

Design. A multicenter, controlled, randomized, open label clinical trial was performed in patients with T2DM in CKD stage 3b-4 (GFR <44 to >15 mL/min/1.73 m2) treated in hospitals of the Mexican Social Security Institute. The follow-up period was at least 1 year from the inclusion of the last patient. The study was conducted in accordance with the provisions of the Declarations of Helsinki and Tokyo with the amendments in Venice (1983). The protocol was approved by the National Research and Ethics Committee and by the Research Committees of all participating hospitals and was registered in National Clinical Trials (NCT03818568).

Patients. Inclusion criteria: Adult patients with T2DM (>18 years) of either sex, with stage 3b-4 of CKD. All patients gave their signed informed consent at the time of recruitment. Exclusion criteria: Previous treatment with KA, kidney transplantation, cancer, HIV-AIDS, or seropositive for hepatitis B or C, patients receiving immunosuppressors, with hypercalcemia, intolerance to KA or disorders of amino acid metabolism. Patients who lost social security during the study, changed address or treating physician were also excluded.

Sample size. Sample size calculation was made on the basis of two independent groups with unequal variances, α=0.05, β=0.20, and assuming a difference of 4.0 mL/min/yr between groups in reduction of eGFR, lower in LPD+KA. Calculation was made with sample size software. A minimum of 51 per group was obtained.

Intervention. Diet design. Energy: 35 kcals/kg of ideal body weight in patients with normal BMI; 30 kcals/kg of ideal body weight in overweight patients (BMI>25 kg/m2) and 40 kcals/kg of ideal weight in underweight patients (BMI<25 kg/m2). Lipids accounted for 35% of the total energy intake (2/3 from polyunsaturated fatty acids). Carbohydrate intake was set at 55-60% of the total energy intake, with >70% of complex carbohydrates. The fiber content was 20-25 g per day. The dietary recommendation for sodium chloride was ~5 g daily and potassium 50-60 mEq/day. Phosphate intake was set at 800-1000 mg per day.

Both groups were prescribed with PrI of 0.6 g/kg/day, preferably plant-based. Patients in LPD+KA group received KA (Ketosteril® (Fresenius Kabi, Deutschland GMBH, BadHomburg, Germany) according to the manufacturer's recommendations (1 tablet/5 kg of body weight divided into 3 doses). All other treatments were provided according to institutional guidelines and prescribed by and according to the criteria of the treating physicians.

Randomization. Patients were centrally randomized 1:1 using an electronic system of random numbers generator.

Outcomes. The primary outcome was: the rate of decline in kidney function (Δ eGFR/year). Secondary outcomes included: start of dialysis, impairment of nutritional status, adverse events, hospitalizations, and mortality.

Follow-up. Patients were followed-up with scheduled visits every two months, for clinical and biochemical evaluation. Blood samples were obtained after an overnight fast, serum and plasma were separated and kept in frozen aliquots (-70 °C) until assay. The 24 h urine volumes were recorded and frozen aliquots stored (-70 °C) until assay. In total blood, hemoglobin, hematocrit, and glycated hemoglobin were measured, and in plasma/serum: glucose, urea, creatinine, albumin, total proteins, triglycerides, total cholesterol, HDL cholesterol, calcium, phosphorus, C-reactive protein. In 24-hour urine: urea and creatinine. Serum Cystatin-C was measured at baseline and months 6, 9 and 12.

Measurements of biochemical parameters were performed on automated equipment using routine techniques. High sensitivity C-reactive protein and Cystatin-C were measured by immunoturbidimetry (Diazyme's Cystatin C Assay. Poway, CA, USA). The protein nitrogen appearance normalized by body weight (nPNA) was calculated with the Maroni formula, GFR was calculated using formulas based on sCr (eCKDCr), and serum Cystatin C (eGFRCysC).

Nutritional evaluations. The patients were evaluated by Nephrology Nutritionists. Nutritional status was monitored by body weight, body mass index, subjective global assessment, body composition analyzed by electrical bioimpedance, and biochemical parameters. As a functional index, the hand grip force was measured with a dynamometer. Treatment adherence was monitored by the 24-hour food intake questionnaire and/or the 3-day food intake diary, nPNA was also used. In the intervention group, adherence to the use of KA was evaluated by counting tablets and packaging at each visit.

Statistical analysis. Data are presented as means and standard deviations or standard errors and as percentages or frequencies according variable characteristics. Differences between groups were analyzed with Chi2 test, or Student´s t test. For calculation of decline of GFR during follow-up, only actual eGFR data were considered, and two-way analyses of variance used. For analysis of the effect of concomitant medication, differences in slopes of regression lines of eGFR over time among users and non-users of specific medication were used. Differences in distribution of adverse events was analyzed with Chi2 and Kolmogorov-Smirnov test. All statistical calculations were made with wSPSS v19 package.