Probiotics and Other Key Determinants of Dietary Oxalate Absorption

Abstract

Oxalate is a common component of many foods of plant origin, including nuts, fruits, vegetables, grains, and legumes, and is typically present as a salt of oxalic acid. Because virtually all absorbed oxalic acid is excreted in the urine and hyperoxaluria is known to be a considerable risk factor for urolithiasis, it is important to understand the factors that have the potential to alter the efficiency of oxalate absorption. Oxalate bioavailability, a term that has been used to refer to that portion of food-derived oxalate that is absorbed from the gastrointestinal tract (GIT), is estimated to range from 2 to 15% for different foods. Oxalate bioavailability appears to be decreased by concomitant food ingestion due to interactions between oxalate and coingested food components that likely result in less oxalic acid remaining in a soluble form. There is a lack of consensus in the literature as to whether efficiency of oxalate absorption is dependent on the proportion of total dietary oxalate that is in a soluble form. However, studies that directly compared foods of varying soluble oxalate contents have generally supported the proposition that the amount of soluble oxalate in food is an important determinant of oxalate bioavailability. Oxalate degradation by oxalate-degrading bacteria within the GIT is another key factor that could affect oxalate absorption and degree of oxaluria. Studies that have assessed the efficacy of oral ingestion of probiotics that provide bacteria with oxalate-degrading capacity have led to promising but generally mixed results, and this remains a fertile area for future studies.

Acute probiotic ingestion reduces gastrointestinal oxalate absorption in healthy subjects

“…The human gastrointestinal tract (GIT) is colonized with different bacterial species that have the ability to degrade oxalate, which has led researchers to suggest a potential therapeutic use of probiotics containing oxalate-degrading bacteria for individuals with increased urinary oxalate excretion [1]. High urinary oxalate (hyperoxaluria) is considered a major risk factor for calcium oxalate kidney stone formation [2].…”

Antinutritional Factors in Plant Foods: Potential Health Benefits and Adverse Effects

“…In ruminants oxalic acid is of only minor significance as an anti-nutritive factor since ruminal microflora can readily metabolize soluble oxalates, and to a lesser extent even insoluble Ca oxalate. While the importance of the anti-nutritive activity of oxalic acid has been recognized for over fifty years it may be a subject of interest to nutritionists in the future [17,18].…”

A Comparison of Two Extraction Methods for Food Oxalate Assessment

“…Oxalate exists in plants in a crystalline form either as calcium oxalate or as a soluble anion (Holmes & Kennedy, 2000). Soluble oxalates, which consist of oxalic acid and soluble salts, can be released when foods are extracted with water; insoluble oxalates, presumed to be mainly calcium oxalate, freely dissolve in acid (Liebman & Al-Wahsh, 2011). Traditionally, dilute acid is used in extracting total oxalate including both the soluble and insoluble fractions.…”

“…Dietary oxalate is mainly derived from foods of plant origin. Efficiency of oxalate absorption depends on the amount present and form (soluble or insoluble), as well as other constituents of the diet such as calcium, magnesium and various fibers (Liebman & Al-Wahsh, 2011). Determination of oxalate content of foods is of special interest for kidney stone patients for whom decreasing urinary oxalate excretion by avoiding consumption of oxalate-rich foods may help prevent stone recurrence (Massey, 2007).…”