AUA 2009 - Stone Disease: Research/New Technology - Effects of Dietary Calcium And Oxalate On Fecal And Urinary Oxalate in Individuals Colonized and not Colonized with Oxalobacter Formigenes - Session Highlights

CHICAGO, IL, USA ( - Colonization with Oxalobacter formigenes has been shown to protect against stone disease, although the exact mechanism remains unknown.

In this important work by Dean Assimos’ group, they examine the interaction between diet, Oxalobacter formigenes numbers and urinary oxalate levels. Controlled diets consisted of increasing amounts of oxalate weekly (50, 250 or 750 mg per day) with calcium fixed at 1000 mg/day or increasing amounts of calcium weekly (400, 1000 or 2000 mg/day) with oxalate fixed at 250 mg/day. The two groups consisted of patients colonized or not colonized with Oxalobacter formigenes, all patients collected their urine and stool. They found that increasing the amount of oxalate in the diet increased the levels of urinary oxalate, while increasing the amount of calcium in the diet decreased the levels of oxalate in the urine. While increasing the amount of oxalate did increase the number of Oxalobacter formigenes in the stool and decrease the amount of oxalate in the fecal water, there was no difference in urinary oxalate in the colonized or uncolonized patients. This suggests that the protective effect of Oxalobacter formigenes colonization may be due to other factors. Thus there may be some protein or cellular wall component that is responsible for this protective effect, which could be isolated and would likely be better accepted by patients than ingestion of whole bacteria.

What this work also shows empirically is that currently, the best way to reduce the levels of urinary oxalate is a diet that contains enough calcium. Unfortunately many stone patients think, or have been told wrongly in the past, that too much calcium in the diet causes stones.

Presented by Dean G. Assimos, MD, et al. at the Annual Meeting of the American Urological Association (AUA) - April 25 - 30, 2009 - McCormick Place Convention Center - Chicago, Illinois, USA.

The opinions expressed in this article are those of the Contributing Medical Editor and do not necessarily reflect the viewpoints of the American Urological Association. Full AUA Conference Coverage