RANDOMIZED CONTROLLED TRIAL OF A LOW ANIMAL PROTEIN, HIGH-FIBER DIET IN THE PREVENTION OF RECURRENT CALCIUM-OXALATE KIDNEY-STONES

Low protein diets are commonly prescribed for patients with idiopathic calcium nephrolithiasis, who account for >80% of new diagnoses of kid ney stones, This dietary advice is supported by metabolic studies and epidemiologic observational studies but has not been evaluated in a co ntrolled trial, Using 1983-1985 data from three Northern California Ka iser Permanente Medical Centers, the authors randomly assigned 99 pers ons who had calcium oxalate stones for the first time to a low animal protein, high fiber diet that contained approximately 56-64 g daily of protein, 75 mg daily of purine (primarily from animal protein and leg umes), one-fourth cup of wheat bran supplement, and fruits and vegetab les. Intervention subjects were also instructed to drink six to eight glasses of liquid daily and to maintain adequate calcium intake from d airy products or calcium supplements. Control subjects were instructed only on fluid intake and adequate calcium intake. Both groups were fo llowed regularly for up to 4.5 years with food frequency questionnaire s, serum and urine chemistry analysis, and abdominal radiography; and they were urged to comply with dietary instructions. In the interventi on group of 50 subjects, stones recurred in 12 (7.1 per 100 person-yea rs) compared with two (1.2 per 100 person-years) in the control group; both groups received a mean of 3.4 person-years of follow-up (p = 0.0 06). After adjustment for possible confounding effects of age, sex, ed ucation, and baseline protein and fluid intake, the relative risk of a recurrent stone in the intervention group was 5.6 (95% confidence int erval 1.2-26.1) compared with the control group, The authors conclude that advice to follow a low animal protein, high fiber, high fluid die t has no advantage over advice to increase fluid intake alone.