Influence of a high-oxalate diet on intestinal oxalate absorption
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Hyperoxaluria is a major risk factor for renal stones. In most cases, it is sustained by increased dietary loads. In healthy individuals with a normal Western diet, the majority of urinary oxalate is usually derived from endogenous metabolism. However, up to 50% may be derived from the diet. We were interested in the effect of a high-oxalate diet on oxalate absorption, not merely on the frequently studied increased oxalate excretion. In study I, 25 healthy volunteers were tested with the [13C2]oxalate absorption test once while following a low-oxalate (63 mg) and once while following a high-oxalate (600 mg) diet for 2 days each. In study II, four volunteers repeated study I, and afterwards continued with a high-oxalate diet (600 mg oxalate/day) for 6 weeks. In the last week, the [13C2]oxalate absorption test was repeated. After 4 weeks of individual normal diet, the oxalate absorption test with a high-oxalate diet was performed again. The results of study I show that the mean [13C2]oxalate absorption under low-oxalate diet was 7.9±4.0%. In the presence of oxalate-rich food, the percent absorption for the soluble labelled oxalate almost doubled (13.7±6.3%). The results of study II show that the mean [13C2]oxalate absorption of the four volunteers under low-oxalate diet was 7.3±1.4%. The absorption increased to 14.7±5.2% under 600 mg oxalate. After 6 weeks under a high-oxalate diet, the [13C2]oxalate absorption was significantly decreased (8.2±1.7%). After the wash-out phase, the absorption was again high (14.1±2.2%) under the 600 mg oxalate challenge.
KeywordsHigh-oxalate diet Low-oxalate diet Oxalate absorption Oxalobacter formigenes
The study was supported in part by a grant of Deutsche Forschungsgemeinschaft (UN91/3). Skilful technical assistance by B. Bär and M. Klöckner is gratefully acknowledged. Dr. S. Voss measured the oxalate content of the diets and foodstuffs and M.E. Schmidt, MD performed the ultrasound examinations.
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