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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASE

September 15-18, 1996
Brussells, Belgium

SCIENTIFIC PROGRAM

Satellite Symposium

Soybean Isoflavones :
Levels in Foods and Pharmacokinetics

Influence of Soybean Processing, Habitual Diet, and Soy Dose on Urinary Isoflavonoid Excretion in Humans
Joanne L. Slavin, Susan C. Karr, Andrea M. Hutchins, Johanna W. Lampe
University of Minnesota, Department of Food Science and Nutrition

In an attempt to explain the wide individual variation seen in urinary isoflavonoid phytoestrogen excretion, we conducted 3 studies: 1) a study comparing fermented and unfermented soy products; 2) a large cross-sectional study of equol production; and 3) a dose response study of urinary isoflavonoid excretion at the low end of soy consumption. All studies were conducted in young, healthy human subjects and urinary isoflavonoids were measured by isotope dilution gas chromatography-mass spectrometry. Fermentation of soy decreased the isoflavone content of the product fed, but increased the urinary isoflavonoid recovery suggesting that fermentation increases availability of isoflavones in soy. Similar to other studies, we found that 35% of screened subjects (30 men and 30 women) excreted equol (>2000 nmol/day). In women, equol excretion was associated with higher intake of dietary fiber and carbohydrate. Finally, when soy protein powder was fed at 0, 5, 10, and 20 g/day (0 to 36 mg isoflavones), there was a linear dose response of urinary isoflavonoid excretion to soy consumption which did not differ between high and low equol excreters. These results suggest that processing of soy does affect isoflavone metabolism and must be considered in recommending isoflavone exposure from soy foods. Secondly, equol excreter status may relate to fermentable carbohydrate content of the diet and needs additional study. Finally, although optimal isoflavone exposure for disease protection has not been established, urinary isoflavonoid excretion appears linear at low to moderate levels of soy consumption.

(Research supported by Minnesota Soybean Research and Promotion Council; soy protein provided by Protein Technologies; tempeh and soybean pieces provided by White Wave Soyfoods, Inc.)

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