Protein Isolate Supplements and Urinary Stone Risk.

Objective: To characterize the lithogenicity associated with consuming specific protein sources, we report a comparative crossover study evaluating the effects of whey, pea, soy, and rice protein isolates on urinary stone risk.

Methods: Volunteers without history of stone disease were recruited for participation. Participants received a 5-day frozen meal plan which included three 20g protein shakes per day. Two 24-hour urine collections were completed on the last two days of each phase. The exact same diet was repeated for subsequent phases, exchanging only the protein isolate in the shake.

Results: Nine participants - 8 male, 1 female - were enrolled with mean age of 24.8 ± 1.6 years and BMI of 22.3 ± 2.2 kg/m2. Urine calcium was significantly lower and pH was higher with pea and soy protein compared to whey protein consumption. Citrate excretion did not differ between any phases compared to whey protein. Urine oxalate was significantly higher in pea phase compared to whey. Supersaturation of calcium oxalate did not differ between any phases compared to whey.

Conclusion: We examined the short-term urinary effect of 4 protein isolates commonly used to supplement high protein diets and found key urinary metabolite differences. These differences were due to varying amino acid profiles but may also be related to differing constituents in each powder, such as cations and unmeasured anions.