Clinical Abstracts: Oxalate Content of Soy Products
Source: Massey LK, et al. Oxalate content of soybean seeds (Glycine max: Leguminosae), soy foods, and other edible legumes. J Agric Food Chem 2001;49:4262-4266.
Funding: Virginia Schafer Fund and Agricultural Research Center Project 3057-0246, Washington State University, and Project 3352 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, Project 3352, Hatch Act and State of Iowa funds, and U.S. Department of Agriculture.
Comments: Eleven cultivars of soybean and 13 commercial soy foods were examined for oxalate content. Among soybean seeds, total oxalate levels ranged from 0.67-3.5 g/100 g dry weight. Commercial soy foods contained 16-638 mg total oxalate per serving (see Table). Soy foods contain substantial amounts of oxalates. High urinary oxalate is associated with increased risk of nephrolithiasis, and patients with calcium oxalate kidney stones are advised to limit total intake of oxalates to 50-60 mg/d. Should stone-formers avoid soy products? The answer is not that simple, because some soy products contain substantial amounts of calcium, which binds oxalates.
Dietary calcium binds oxalates in the gastrointestinal tract and is actually associated with decreased risk of kidney stones.1,2 Supplemental calcium, however, was associated with increased incidence of renal stones (relative risk 1.20) in the Nurse’s Health Study, possibly because supplements were not consumed with meals; two thirds of those who took calcium took the supplements between meals or with low-oxalate meals.1
The primary form of oxalate found in soybeans is calcium oxalate, an insoluble form. However, up to 10 % of calcium oxalate is absorbed by healthy volunteers. Additionally, soy contains lesser amounts of soluble oxalates (bound to potassium or sodium in the range of 14.7-29.9 mg/100 g).
The current analysis found a wide range of oxalate content even among similar products. The best test would be a trial designed to examine actual absorption of oxalates from soy foods in humans. No such trial has been performed, although an absorption study found that 3.8% of total oxalates were absorbed from peanuts. Until an adequate clinical trial is performed, the most cautious course of action would be to inform recurrent calcium oxalate stone-formers that soy products are high in oxalates and should be consumed in moderation.
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Table |
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Oxalates and calcium content of soy foods* |
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Breakfast links 69 mg/14 mg Lentils, cooked 100 mg/16 mg Peanut butter 225 mg/10 mg Refried beans 193 mg/27 mg Soy beverage 336 mg/122 mg Soy burger 58 mg/48 mg Soy cheese 16 mg/nondetectable Soy nuts 392 mg/56 mg Soy yogurt 113 mg/nondetectable Tempeh 23 mg/77 mg Textured vegetable protein 496-638 mg/nondetectable-204 mg Tofu prepared with calcium 116-235 mg/nondetectable-247 mg Tofu prepared with magnesium 43-94 mg/nondetectable-60 mg
*Amount presented per serving of oxalates and calcium, respectively |
References
1. Curhan GC, et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med 1997;126:497-504.
2. Curhan GC, et al. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993; 328:833-838.
Fugh-Berman A. Oxalate content of soy products. Altern Ther Women's Health 2002;4(12):96.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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