Submitted to: American Society for Bone and Mineral Research
Publication Type: Abstract Only
Publication Acceptance Date: 10/20/2001
Publication Date: 4/21/2002
Citation: MASSEY, L.K., GRENTZ, L.M., HORNER, H.T., PALMER, R.G. SOYBEAN AND SOYFOOD CONSUMPTION INCREASES URINARY CALCIUM AND OXALATE EXCRETION. AMERICAN SOCIETY FOR BONE AND MINERAL RESEARCH. 2002. Abstract No. M476. Interpretive Summary:
Technical Abstract: Soybeans and commonly consumed soyfoods, such as tofu, soy beverage and textured vegetable protein (TVP), contain over 110 umol (10 mg) oxalate per serving, primarily in the form of calcium oxalate. Human absorption of oxalate from soyfoods is unstudied, so the potential of their consumption to increase urinary oxalate, and therefore risk of calcium oxalate stone formation, is unknown. This study examined oxalate absorption from soybeans and soyfoods by measuring changes in urinary oxalate excretion. Eight healthy individuals with no prior history of kidney stones participated in eight oxalate load (OL) tests comprised of two soybean lines, five soyfoods and a 8.3 mmol sodium oxalate solution. Pre-load and post-load urines were analyzed for calcium and oxalate and expressed as a ratio to creatinine. The increase in 8 hour post-load urinary Ca excretion ranged from 0.70 +/ 0.40 mmol from the magnesium precipitated tofu to 1.29 +/ 1.13 mmol Ca from the Ca precipitated tofu load. Ca absorption from th soybean and soyfoods ranged from 7.6 +/ 4.3 to 13.1 +/ 10.9%. Increases in urinary oxalate excretion ranged from 19.6 +/ 23.3 to 124 +/ 156 mmol. Absorption ranged from 2.1 +/ 2.1% from high oxalate soybean line L95-1409 to 5.4 +/ 4.2% from soynuts. Individual increases varied widely, from zero to 481 umol. Since normal urinary oxalate excretion is defined as 110 to 440 umol per day, the inclusion of soybeans and soyfoods in the diet is capable of increasing urinary oxalate excretion to 450 umol (40 mg) or more per day, a concentration defined as hyperoxaluria. Thus, frequent consumption of soybeans and soyfoods may be a risk factor for calcium-oxalate kidney stone formation in susceptible individuals, such as those with a prior history of calcium stones or high normal oxalate levels.