A randomized trial of low-animal-protein or high-fiber diets for secondary prevention of calcium nephrolithiasis.

BACKGROUND: The purpose of this trial was to evaluate the efficacy of a low-animal-protein diet (LAPD) or a high-fiber diet (HFD) for the prevention of calcium nephrolithiasis recurrence. METHODS: We conducted a 4-year randomized trial comparing the effect of 2 diets in 175 idiopathic calcium stone formers. Fifty-five were assigned to a LAPD (<13% of total energy derived from protein), 60 were assigned to a HFD (>25 g/day fiber) and 60 were placed on a normal diet (control group). The primary outcome measure was the time to the first recurrence of calcium nephrolithiasis. Daily urine compositions were analyzed at baseline, at month 4 (M4), M12, M24, M36 and M48. RESULTS: Seventy-three patients completed the trial (23 in the LAPD group, 27 in the HFD group and 23 in the control group). Recurrence was 48% (11/23) in the LAPD group, 63% (17/27) in the HFD group and 48% (11/23) in the control group (p = not significant). During follow-up, urinary calcium levels and other urine parameters did not change significantly in the 3 groups, except for a significant decrease in 24-hour urinary sulfate in the LAPD group. CONCLUSIONS: In idiopathic calcium stone formers, neither a LAPD nor a HFD appeared to provide protection against recurrence.

A randomized trial of low-protein diet in type 1 and in type 2 diabetes mellitus patients with incipient and overt nephropathy.

OBJECTIVE: The efficacy of a low-protein diet in the secondary prevention of diabetic nephropathy is not established in patients with type 1 or type 2 diabetes mellitus. To determine whether a low-protein diet slows the decrease in glomerular filtration rate (GFR) and decreases the albumin excretion rate (AER) in diabetic patients with incipient and overt nephropathy, we performed a 2-year prospective, randomized controlled trial comparing the effects of a low-protein diet (0.8 g/kg/day) with a usual-protein diet. SETTING AND PATIENTS: The study was conducted in a University hospital and included 63 type 1 and type 2 diabetic patients with either incipient or overt nephropathy and mild renal failure (prestudy GFR, 80 +/- 20 mL/min). The primary outcome measures were decreased in GFR and 24-hour AER. RESULTS: In the low-protein-diet group, patients were younger (52 +/- 12 versus 63 +/- 9 years old) and more often were type 2 diabetic. During the follow-up period, according to dietary records the low-protein-diet group consumed 16% +/- 3% of total caloric intakes as compared with 19% +/- 4% in the usual-protein-diet group (P < .02), but 24-hour urinary urea excretions did not differ between the two groups. The 2-year GFR decrease was 7 +/- 11 mL/min in the low-protein-diet group and 5 +/- 15 mL/min in the usual-protein-diet group (P = not significant). AER did not increase significantly in the two diet groups during the follow-up period. Blood pressure and glycemic control were similar in the two groups all along the study. The decrease in GFR and AER were also similar in 6 compliant patients according to dietary records and to 24-hour urinary urea excretions from the low-protein-diet group and in 12 patients from the usual-protein-diet group. CONCLUSIONS: A 2-year low-protein diet did not alter the course of GFR or of AER in diabetic patients with incipient or overt nephropathy receiving renin-angiotensin blockers with strict blood pressure control.