Isoflavone Concentration in Soyfoods

Isoflavones are found in soyfoods both with and without a sugar molecule attached. The two primary isoflavones in soybeans are daidzein and genistein and their respective glucosides, genistin and daidzin. Soyfoods typically contain more genistein than daidzein, although this ratio varies among different soy products.

On a dry weight basis, raw soybeans contain between two and four milligrams of total isoflavones/gram. Soyfoods differ somewhat in their concentration of isoflavones, but all of the traditional soyfoods, such as tofu, soy milk, tempeh and miso, are rich sources of isoflavones providing about 30 to 40 milligrams per serving. One-half cup of soy flour contains approximately 50 milligrams of isoflavone. Only two soy products, soy sauce and soyoil, do not contain isoflavones.

Soy protein concentrates (<65% soy protein), a widely used ingredient (frequently used in soy burgers), may or may not contain nutritionally significant amounts of isoflavones depending on how the product was processed. However, isoflavone levels in the most commonly used soy protein concentrates are very low. Both soy flour and textured soy protein are rich in isoflavones. Soy protein isolate (<90% soy protein) contains less than these products but still has significant amounts.

For those interested in the full benefits of soy isoflavones, newer naturally concentrated products are available with much better flavor than retail soy products. Because of a patented, natural concentration process, just 1 Revival Soy bar or shake contains the amount of isoflavones found in 6 cups of a typical soymilk. Learn more.

A group of soyfoods, often referred to as second generation products (such as soy hot dogs and soy-based ice cream) can have much lower amounts of isoflavones because they frequently contain considerable amounts of non-soy ingredients.

Estimated Values for Isoflavone Content of Selected Soyfoods*

(This information was distributed as part of a presentation at the American Dietetic Association 80th Annual Meeting and Exhibition, held October 27-30, 1997, in Boston, Massachusetts, by James W. Anderson, M.D. Professor of Medicine and Clinical Nutrition University of Kentucky, Lexington, KY. Phone 606-281-4954; fax 606-233-3832, e-mail: jwandersmd@aol.com.

Food Svg Size(g) Serving Size Measure Protein(g/100g) Genistein(ug/g prot) Total Isoflavone(ug/g prot) Isoflavone(mg/g prot) mg/svg
Mature soybeans, uncooked 93 1/2 cup 37.0 1106 1891 5.1 175.6
Roasted soybeans 86 1/2 cup 35.2 1214 1942 5.5 167.0
Soy flour 21 1/4 cup 37.8 1185 2084 5.5 43.8
Textured soy protein, dry 30 1/4 cup 18.0 472 928 5.2 27.8
Green soybeans,uncooked 128 1/2 cup 16.6 301 548 3.3 70.1
Soy milk 228 1 cup 4.4 30 56 2.0 20.0
Tempeh, uncooked 114 4 oz 17.0 277 531 3.1 60.5
Tofu, uncooked 114 4 oz 15.8 209 336 2.1 38.3
Soy isolate, dry 28 1 oz 92.0 1100 2174 2.2 56.5
Soy concentrate, dry 28 1 oz 63.6 111 195 0.3 12.4

These values were obtained from the published literature and from analyses we have obtained for selected products. The isoflavone content varies widely among soybean varieties and from product to product based on manufacturing process and source of soy protein. These estimates are our best calculation of isoflavone values provided by currently available products. The references listed below provide more detailed information about the different isoflavones in specific products.

References:

  1. Coward L, Barnes NC, Setchell KDR, Barnes S. Journal of Agricultural and Food Chemistry 1993; 41:1961-67.
  2. Dwyer JT, Goldin BR, Saul N, Gualtieri L, Barakat S, Adlercreutz H. Journal of the American Dietetic Association 1994; 94: 739-43.
  3. Franke AA, Custer LJ, Cerna CM, Narala KK. Journal of Agricultural and Food Chemistry 1994; 42: 1905-13.
  4. Reinli K, Block G. Nutrition and Cancer 1996; 26: 123-48.
  5. Wang H, Murphy PA. Journal of Agricultural and Food Chemistry 1994; 42: 1666-1673.

Questions may be directed to:

Dr. James Anderson,
B402 VA Medical Center 111C
2250 Leestown Rd.
Lexington, KY 40511
janders@pop.uky.edu
jwandersmd@aol.com

or

Belinda Smith, MD, MS, RD
606/233-4511, x 4431
sbelin0@pop.uky.edu

or

Carla Green, RD
606/233-4511, x 4427
csgree1@pop.uky.edu