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ARS Home » Midwest Area » Ames, Iowa » Corn Insects and Crop Genetics Research » Research » Publications at this Location » Publication #123632
Title: HIGH LEVELS OF OXALATE IN SOYBEAN SEEDS AND SOYFOODS MAY INCREASE HUMAN CALCIUM OXALATE KIDNEY STONE RISK

Author
item MASSEY, LINDA - WASHINGTON STATE UNIV
item GRENTZ, LISA - WASHINGTON STATE UNIV
item Palmer, Reid
item HORNER, HARRY - IOWA STATE UNIVERSITY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/7/2001
Publication Date: 7/7/2001
Citation: MASSEY, L.K., GRENTZ, L.M., PALMER, R.G., HORNER, H.T. HIGH LEVELS OF OXALATE IN SOYBEAN SEEDS AND SOYFOODS MAY INCREASE HUMAN CALCIUM OXALATE KIDNEY STONE RISK. FOURTH INTERNATIONAL SOY AND HEALTH CONFERENCE. 2001. ABSTRACT NO. 16.

Interpretive Summary:

Technical Abstract: Raw soybeans and common soyfoods, such as tofu, soy beverage, soynuts and textured vegetable protein (TVP), contain over 110 umol (10 mg) oxalate per serving. Oxalate in soybean seeds is primarily in the form of calcium oxalate crystals. Eleven soybean cultivars showed relatively high levels of total seed oxalate, from 0.67 g to 3.5 g/100 g dry weight. Oxalate is retained during processing as shown by the 182 to 7250 umol (16 to 638 mg) oxalate per serving in 13 tested commercial soyfoods. Calcium oxalate is considered insoluble, so it was previously assumed that the oxalate could not be absorbed. However, Hayes et al. (1999) described absorption of calcium oxalate in rats. The present study examined human oxalate absorption from soybean seeds and soyfoods after consumption by measuring changes in urinary oxalate excretion. Eight healthy individuals with no history of kidney stones consumed eight oxalate feedings comprised of seeds sfrom two soybean lines, five soyfoods (2 tofus, soy beverage, textured vegetable protein and soynuts) and 8.3 mmol sodium oxalate in solution. After correction for pre-load baseline excretion, increases in urinary oxalate ranged from 19.6 +/- 23.3 to 124 +/- 156 umol for the seeds of two soybean lines and five soyfoods during the eight hours after ingestion of each oxalate load. Absorption ranged from 2.1 +/- 2.1% from one high-oxalate soybean line to 5.4 +/- 4.2% from soynuts. Since normal urinary oxalate excretion is defined as 110 to 440 umol (10 to 39 mg) per day, frequent consumption of soybeans and soyfoods in the diet may increase urinary oxalate excretion to 450 umol (40 mg) or more per day, a concentration defined as hyperoxaluria, which is a risk factor for calcium-oxalate kidney stone formation in susceptible individuals.