Cianciaruso 2008a.

Study characteristics
Methods	Study design: parallel RCT Study duration: January 1999 to December 2006 Study follow‐up period: Mean 13 ± 4 months (6 to 18 months)
Participants	Country: Italy Setting: single centre University Hospital CKD clinic Patients aged ≥ 18 years with eGFR ≤ 30 mL/min/1.73 m2; stable kidney function for at least 3 months Number (randomised/evaluated for primary outcome (serum urea nitrogen concentration)): low protein diet group (212/200); normal protein diet group (211/192) Mean age ± SD (years): low protein diet group (62 ± 18); normal protein diet group (62 ± 18) Sex (M/F): low protein diet group (112/88); normal protein diet group (110/82) Exclusion criteria: unstable kidney function; malignant disease; treatment with immunosuppressive drugs; UPE > 5 g/24 h; pregnancy
Interventions	Low protein diet group Prescribed protein intake: 0.55 g/kg/day Calculated protein intake at 12 months: 0.63 ± 0.13 g/kg/day Normal protein diet group Prescribed protein intake: 0.8 g/kg/day Calculated protein intake at 12 months: 0.88 ± 0.06 g/kg/day Co‐interventions Calorie intake 30 Kcal/kg/day Overweight participants were prescribed 25 kcal/kg/day Daily multivitamin and mineral tablet Dietary sodium intake restricted to 2.5 g/day Calcium supplements to guarantee calcium intake of 1000 to 1500 mg/day Iron supplementation (200 mg/day oral element iron) as required to maintain transferrin saturation ≥ 20%
Outcomes	ESKD (commencement of dialysis) Death (all causes) Monthly decrease in eGFR (eGFR calculated from MDRD equation) Body weight Protein‐calorie malnutrition (body weight loss > 5% in one month or 7.5% in 3 months or BMI < 20 kg/m2 + albumin < 3.2 g/dL + normal CRP)
Notes	Funding source: Italian Ministry of University & Scientific Research (PRIN‐2001; Grant 061427) Contact with study authors for additional information: no Other: patient survival/ESKD at 12 month and average follow up of 32 months also provided
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Simple randomised list, which was concealed from investigators
Allocation concealment (selection bias)	Low risk	Numbered opaque sealed envelopes opened in sequence by administration staff personnel not involved in patient care
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not blinded and lack of blinding may influence patient management
Blinding of outcome assessment (detection bias): End or change in GFR End of change in GFR	Low risk	Laboratory measure & calculation (eGFR measured by MDRD formula) unlikely to be influenced by lack of blinding
Blinding of outcome assessment (detection bias): Need to start dialysis Need to start dialysis	Low risk	Single centre study with same criteria for commencing dialysis (eGFR = 6 mL/min/1.73 m2, hyperkalaemia, fluid overload, malnutrition)
Incomplete outcome data (attrition bias) All outcomes	Low risk	All patients accounted for; 9/423 (2%) lost to follow‐up at mean 13 months; 15/423 (3.5%) lost to follow‐up by 4 years
Selective reporting (reporting bias)	Low risk	All expected outcomes (death, commencement of dialysis, GFR, protein‐calorie malnutrition) reported
Other bias	Low risk	Investigator driven. Partially funded by grant from Italian Ministry of University & Scientific Research (PRIN‐2001; Grant 061427)