Microbial oxalate degradation: Effects on oxalate and calcium balance in humans

Abstract

Three, 4-wk, controlled feeding periods were used to assess relationships between oxalate excretion, calcium balance, and numbers of oxalate-degrading bacteria during consumption of a baseline diet, and the baseline diet with the addition of 175 g spinach or 260 g broccoli by 8 premenopausal women. Oxalate intakes were 108, 100 and 1570 mg/day during consumption of the baseline, broccoli, and spinach diets, respectively. Numbers of oxalate-degrading bacteria (ODB) ranged from 10 6–10 7/g feces in 5 subjects whereas no oxalate-degrading bacteria (no-ODB) were detected in 3 subjects. Four of the 5 ODB subjects exhibited an increase (p<0.05) in bacterial numbers, ranging from 5-to 14-fold, during the spinach consumption period compared to the numbers found during baseline diet consumption, which suggested that humans can adapt to high oxalate feeding via increased numbers of oxalate degraders. There was a relationship between the presence of oxalate-degrading bacteria and unrecovered oxalate, as ODB subjects had a higher (p<0.01) mean unrecovered oxalate than did no-ODB subjects during each dietary treatment period. Mean calcium balance was lower (p<0.05) for no-ODB than for ODB subjects during consumption of the baseline and broccoli diets, but not significantly different during the spinach consumption period. The possibility of a relationship between the presence of oxalate-degrading microorganisms and calcium availability is discussed.