Don’t Judge This Wonder-Bean Too Quickly
How Does Soy Protein Stack Up?
Soy protein is a complete protein – it contains all of the essential amino acids required for human growth and maintenance. Proteins are evaluated by a “protein digestibility corrected amino acid score” (PDCAA). This score rates proteins for their amino acid content and the body’s ability to digest and absorb these amino acids when compared to a standard: egg whites. Egg whites have a PDCAA score of 1. Soy protein, whey protein and milk (casein) also have a PDCAA of 1.
Soy protein offers heart-health benefits. In October 1999, the FDA issued its final rule allowing claims that 25 grams of soy protein per day is associated with a lower risk of coronary heart disease.(1,2) The basis of this health claim is that lower blood levels of total cholesterol and low density lipoprotein (LDL) can be achieved by substituting soy protein for animal protein.(3,4)
Isoflavones Offer Health Benefits
Soy protein naturally contains compounds called isoflavones. These phytoestrogens (plant estrogens) can bind to estrogen receptors in the body and exhibit weak estrogen-promoting and estrogen-inhibiting activity.(5) Isoflavones also provide antioxidant activity.
• Population studies suggest that soy consumption is associated with a lowered risk of breast cancer.(6,7) Women of Asian descent have a lower incidence of breast cancer than women in Western countries.
• Isoflavones in soy may offer a protective effect against hormonally regulated cancer.(8)
• Soy isoflavones are reported to help reduce menopausal symptoms.(9,10) In fact, isoflavones have been favorably compared to estrogen hormone replacement therapy (HRT) in reducing menopausal symptoms but without the negative side effect of increasing breast cancer risk.(11)
• Soy isoflavones appear to modestly protect bone loss. Studies show isoflavone-rich soy protein can increase bone mineral density (BMD) while reducing BMD loss.(12,13)
• Isoflavones also offer a protective benefit to men. Studies show that supplementing with soy isoflavones appears to reduce the risk of developing prostate cancer and may also help reduce symptoms associated with prostate cancer.(14, 15)
• Soy isoflavones have also been shown to reduce side effects in children receiving either chemotherapy or radiation treatments.(16)
While it is clear the phytoestrogens in soy offer protective health benefits, people with serious medical conditions, including cancer of the breast, ovary or prostate, should consult their health care practitioner before using soy.
The Importance of Proper Processing
Like all legumes, soybeans must be processed by soaking, heat, steam, pressure, or mechanical extraction to facilitate digestion of the protein contained in the bean. Heating and mechanical extraction (soaking, milling and fermenting) perform three important functions in soy preparation:
1. Soaking inactivates phytate (phytic acid), an indigestible form of inositol that can hinder the absorption of minerals in the diet.
2. Heating degrades and inactivates trypsin inhibitors.(17) These are found in all legumes in small amounts, and they prevent normal digestive processes in the body.
3. Heating and fermenting deactivates agglutinins. Agglutinins in foods can promote blood clotting. Soy products generally do not contain agglutinins because they are deactivated during heat processing. Soy flour that has not been heated may contain agglutinins.
Soy protein is a safe and healthful dietary supplement. The pharmacological properties of isoflavones are strongly supported for their health benefits. Soy protein is a sustainable source of protein and a healthful solution to meeting daily energy needs.
Putting Rumors to Rest
Thyroid function is not impaired by soy protein.(18,19) Soy protein does not impede iodine absorption by the body. Clinical trials show that soy protein rich in isoflavones (19 g soy, 36 mg isoflavones) did not have any effect on thyroid-stimulating hormone (TSH) or thyroxine in men or women.(20,21) People who are predisposed to hypothyroidism do not need to avoid soy, but they should ensure adequate intake of iodine and thyroid hormone medications.(19)
Consumers who wish to avoid risks can be assured that NSP uses only non-GMO soy.
2) Bakhit RM, Klein BP, Essex-Sorlie D, et al. Intake of 25 g of soybean protein with or without soybean fiber alters plasma lipids in men with elevated cholesterol concentrations. J Nutr 1994;124:213-22.
3) Potter SM, Baum JA, Teng H, et al. Soy protein and isoflavones: their effects on blood lipids and bone density in postmenopausal women. Am J Clin Nutr 1998;68:1375S-9S.
4) Wong WW, Smith EO, Stuff JE, et al. Cholesterol-lowering effect of soy protein in normocholesterolemic and hypercholesterolemic men. Am J Clin Nutr 1998;68:1385S-9.
5) Hendler SS Ph.D., M.D., Rorvik D M.S. PDR for Nutritional Supplements 1st Edition. New Jersey: Medical Economics Company, Inc.; 2001.
6) Keinan-Boker L, van Der Schouw YT, Grobbee DE, Peters PH. Dietary phytoestrogens and breast cancer risk. Am J Clin Nutr 2004;79:282-8.
7) Sartippour MR, Rao JY, Apple S, et al. A pilot clinical study of short-term isoflavone supplements in breast cancer patients. Nutr Cancer 2004;49:59-65.
8) Trock BJ, Hilakivi-Clarke L, Clarke R. Meta-analysis of soy intake and breast cancer risk. J Natl Cancer Inst 2006;98:459-71.
9) Washburn S, Burke GL, Morgan T, et al. Effect of soy protein supplementation on serum lipoproteins, blood pressure, and menopausal symptoms in perimenopausal women. Menopause 1999;6:7-13.
10) Albertazzi P, Pansini F, Bonaccorsi G, et al. The effect of dietary soy supplementation on hot flushes. Obstet Gynecol 1998;91:6-11.
11) Barnes S. Phyto-oestrogens and osteoporosis: what is a safe dose? Br J Nutr. 2003 Jun;89 Suppl 1:S101-8.
12) Ho SC, Chan SG, Yi Q, et al. Soy intake and the maintenance of peak bone mass in Hong Kong Chinese women. J Bone Miner Res 2001;16:1363-9.
13) Cassidy A, Albertazzi P, Lise Nielsen I, Hall W, Williamson G, Tetens I, Atkins S, Cross H, Manios Y, Wolk A, Steiner C, Branca F. Proc Nutr Soc. 2006 Feb;65(1):76-92.Critical review of health effects of soybean phytoestrogens in post-menopausal women.
14) Kumar NB, Cantor A, Allen K et al. The specific role of isoflavones in reducing prostate cancer risk. Prostate 2004;59:141-7.
15) Jacobsen BK, Knutsen SF, Fraser GE. Does high soy milk intake reduce prostate cancer incidence? The Adventist Health Study. Cancer Causes Control 1998;9:553-7.
16) Hernández-Infante M, Sousa V, Montalvo I, Tena E. Impact of microwave heating on hemagglutinins, trypsin inhibitors and protein quality of selected legume seeds. Plant Foods Hum Nutr. 1998;52(3):199-208.
17) Tacyildiz N, Ozyoruk D, Yavuz G, Unal E, Dincaslan H, Dogu F, Sahin K, Kucuk O. Soy isoflavones ameliorate the adverse effects of chemotherapy in children.Nutr Cancer. 2010;62(7):1001-5.
18) Hampl R, Ostatnikova D, Celec P, Putz Z, Lapcík O, Matucha P. Short-term effect of soy consumption on thyroid hormone levels and correlation with phytoestrogen level in healthy subjects. Endocr Regul. 2008 Jun;42(2-3):53-61
19) Messina M, Redmond G Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid. 2006 Mar;16(3):249-58.
20) Zhou Y, Alekel DL, Dixon PM, Messina M, Reddy MB. The Effect of Soy Food Intake on Mineral Status in Premenopausal Women. J Womens Health (Larchmt). 2011 Apr 12. [Epub ahead of print]
21) Dillingham BL, McVeigh BL, Lampe JW, Duncan AM. Soy protein isolates of varied isoflavone content do not influence serum thyroid hormones in healthy young men. Thyroid. 2007 Feb;17(2):131-7