Influence of a high-oxalate diet on intestinal oxalate absorption

Abstract

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.

Evidence for net renal tubule oxalate secretion in patients with calcium kidney stones

“…This could be due to the relatively low oxalate content of the study diet; however, there is experimental evidence for increased fractional GI absorption of oxalate with lower oxalate intake (13), although this is controversial (37,44). Notably, the secretory trait in our population of stone formers was stable whether in the fasting or fed state.…”

Enteric hyperoxaluria, recurrent urolithiasis, and systemic oxalosis in patients with Crohn’s disease

“…Conservative treatment options are still scarce and only a high fluid intake (> 1.5 l per 1.73 m 2 /day) plus careful dietary advice (low-oxalate and slightly enriched calcium diet) are the current therapeutic measures [4,32]. ESRF and systemic oxalosis often develop early, especially in those patients with multiple bowel resections.…”

Determinants of 24-hour Urinary Oxalate Excretion

“…Estimates of the proportion of urinary oxalate derived from dietary oxalate vary widely (generally between 10% and 50% (7)). In addition, some loading studies suggest that absorption of oxalate is much higher at low intakes (7), whereas others describe a constant relationship (28) or report higher absorption with higher oxalate intake (29). Part of a Adjusted for age, kidney stone history, cohort, weight (continuous), 24-h urinary excretion of creatinine, potassium, magnesium, and phosphorus (all in quartiles), dietary oxalate (quartiles), supplemental calcium intake (four categories), and total intake of vitamin C (five categories).…”