What Are Star Ratings?
Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.
For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
3 Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2 Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1 Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.
This supplement has been used in connection with the following health conditions:
How It Works
How to Use It
The ideal intake of soy is not known. Researchers suggest the equivalent of one serving of soy foods per day supports good health, and the benefits increase as soy intake increases.21 Societies in which large amounts of soy are consumed ingest between 50 and 100 mg per day of soy isoflavones. The cholesterol -lowering effects of soy have been observed at amounts as low as 20 grams of soy protein per day, if it replaces animal protein in the diet.22
Where to Find It
Relatively large amounts of isoflavones are present in whole soybeans, roasted soy nuts, tofu, tempeh, soy milk, meat substitutes, soy flour, and some soy protein isolates. In addition, the isoflavones present in soy are available as supplements, in capsules or tablets.
Although deficiencies do not occur, people who do not consume soy foods will not gain the benefits of soy.
Interactions with Supplements, Foods, & Other Compounds
Soy contains a compound called phytic acid , which can interfere with mineral absorption.
Interactions with Medicines
Certain medicines interact with this supplement.
Types of interactions: Beneficial Adverse Check
Replenish Depleted Nutrients
Reduce Side Effects
Potential Negative Interaction
The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.
Soy products and cooked soybeans are safe at a wide range of intakes. However, a small percentage of people have allergies to soybeans and thus should avoid soy products.
Soy isoflavones have been reported to reduce thyroid function in some people.29 A preliminary trial of soy supplementation among healthy Japanese, found that 30 grams (about one ounce) per day of soybeans for three months, led to a slight reduction in the hormone that stimulates the thyroid gland.30 Some participants complained of malaise, constipation , sleepiness, and even goiter . These symptoms resolved within a month of discontinuing soy supplements. However, a variety of soy products have been shown to either cause an increase in thyroid function31 or produce no change in thyroid function.32 The clinical importance of interactions between soy and thyroid function remains unclear. However, in infants with congenital hypothyroidism , soy formula must not be added, nor removed from the diet, without consultation with a physician, because ingestion of soy may interfere with the absorption of thyroid medication.33
Most research, including animal studies, report anticancer effects of soy extracts,34 though occasional animal studies have reported cancer-enhancing effects.35 The findings of several recent studies suggest that consuming soy might, under some circumstances, increase the risk of breast cancer . When ovaries have been removed from animals—a situation related to the condition of women who have had a total hysterectomy—dietary genistein has been reported to increase the proliferation of breast cancer cells.36 When pregnant rats were given genistein injections, their female offspring were reported to be at greater risk of breast cancer.37 Although premenopausal women have shown decreases in estrogen levels in response to soy,38 , 39 pro-estrogenic effects have also been reported.40 When pre-menopausal women were given soy isoflavones, an increase in breast secretions resulted—an effect thought to elevate the risk of breast cancer.41 In yet another trial, healthy breast cells from women previously given soy supplements containing isoflavones showed an increase in proliferation rates—an effect that might also increase the risk of breast cancer.42
Of 154 healthy postmenopausal women who received 150 mg of soy isoflavones per day for five years, 3.9% developed an abnormal proliferation of the tissue that lines the uterus (endometrial hyperplasia). In contrast, none of 144 women who received a placebo developed uterine hyperplasia.43 Although no case of uterine cancer was diagnosed during the study, endometrial hyperplasia is a potential forerunner of uterine cancer. The amount of isoflavones used in this study is two to three times as much as that used in many other studies. Nevertheless, the possibility exists that long-term use of isoflavones could cause uterine hyperplasia, and women taking isoflavones should be monitored appropriately by their doctor.
Some postmenopausal women taking the soy isoflavone genistein have experienced gastrointestinal side effects (abdominal pain, epigastric pain, dyspepsia, vomiting, or constipation).44
1. Carrol KK, Kurowska EM. Soy consumption and cholesterol reduction: review of animal and human studies. J Nutr 1995;125:594–7S.
2. Crouse JR 3rd, Morgan T, Terry JG, et al. A randomized trial comparing the effect of casein with that of soy protein containing varying amounts of isoflavones on plasma concentrations of lipids and lipoproteins. Arch Intern Med 1999;159:2070–6.
3. Nestel PJ, Yamashita T, Sasahara T, et al. Soy isoflavones improve systemic arterial compliance but not plasma lipids in menopausal and perimenopausal women. Arterioscler Thromb Vasc Biol 1997;17:3392–8.
4. Samman S, Lyons, Wall PM, et al. The effect of supplementation with isoflavones on plasma lipids and oxidisability of low density lipoprotein in premenopausal women. Atherosclerosis 1999;147:277–83.
5. Hoie LH, Morgenstern EC, Gruenwald J, et al. A double-blind placebo-controlled clinical trial compares the cholesterol-lowering effects of two different soy protein preparations in hypercholesterolemic subjects. Eur J Nutr 2005;44:65–71.
6. Washburn S, Burke GL, Morgan T, Anthony M. Effect of soy protein supplementation on serum lipoproteins, blood pressure, and menopausal symptoms in perimenopausal women. Menopause1999;6:7–13.
7. Rivas M, Garay RP, Escanero JF, et al. Soy milk lowers blood pressure in men and women with mild to moderate essential hypertension. J Nutr 2002;132:1900–2.
8. Burke V, Hodgson JM, Beilin LJ, et al. Dietary protein and soluble fiber reduce ambulatory blood pressure in treated hypertensives. Hypertension2001;38:821–6.
9. He J, Gu D, Wu X, et al. Effect of soybean protein on blood pressure: a randomized, controlled trial. Ann Intern Med 2005;143:1–9.
10. Welty FK, Lee KS, Lew NS, Zhou JR. Effect of soy nuts on blood pressure and lipid levels in hypertensive, prehypertensive, and normotensive postmenopausal women. Arch Intern Med 2007;167:1060–7.
11. Esmarck B, Andersen JL, Olsen S, et al. Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans. J Physiol 2001;535:301–11.
12. Stroescu V, Dragan J, Simionescu L, Stroescu OV. Hormonal and metabolic response in elite female gymnasts undergoing strenuous training and supplementation with SUPRO Brand Isolated Soy Protein. J Sports Med Phys Fitness 2001;41:89–94.
13. Casini ML, Marelli G, Papaleo E, Ferrari A, D'Ambrosio F, Unfer V. Psychological assessment of the effects of treatment with phytoestrogens on postmenopausal women: a randomized, double-blind, crossover, placebo-controlled study. Fertil Steril 2006;85:972-8.
14. Upmalis DH, Lobo R, Bradley L, Warren M, Cone FL, Lamia CA. Vasomotor symptom relief by soy isoflavone extract tablets in postmenopausal women: a multicenter, double-blind, randomized, placebo-controlled study. Menopause 2000;7:236-42.
15. Bhathena SJ, Velasquez MT. Beneficial role ofdietary phytoestrogens in obesity and diabetes. Am J Clin Nutr2002;76:1191–201[review].
16. Allison DB, Gadbury G, Schwartz LG, et al. Anovel soy-based meal replacement formula for weight loss among obeseindividuals: a randomized controlled clinical trial. Eur J Clin Nutr2003;57:514–22.
17. Bosello O,Cominancini L, Zocca I, et al. Short- and long-term effects of hypocaloric dietscontaining proteins of different sources on plasma lipids and apoproteins ofobese subjects. Ann Nutr Metab 1988; 32:206–14.
18. Yamashita T, Sasahara T, Pomeroy SE, et al. Arterial compliance, bloodpressure, plasma leptin, and plasma lipids in women are improved with weight reduction equally with a meat-based diet and a plant-based diet. Metabolism1998;47:1308–14.
19. Jenkins DJ, Wolever TM, Spiller G, et al. Hypocholesterolemic effect ofvegetable protein in a hypocaloric diet. Atherosclerosis 1989;78:99–107.
20. Bryant M, Cassidy A, Hill C, et al. Effect of consumption of soy isoflavones on behavioural, somatic and affective symptoms in women with premenstrual syndrome. Br J Nutr 2005;93:731–9.
21. Messina M. To recommend or not to recommend soy foods. J Am Diet Assoc 1994;94:1253–4.
22. Teixeira SR, Potter SM, Weigel R, et al. Effects of feeding 4 levels of soy protein for 3 and 6 wk on blood lipids and apolipoproteins in moderately hypercholesterolemic men. Am J Clin Nutr 2000;71:1077–84.
23. Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: The influence of soy-based formulas. J Am Coll Nutr 1997;16:280–2.
24. Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: The influence of soy-based formulas. J Am Coll Nutr 1997;16:280–2.
25. Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: The influence of soy-based formulas. J Am Coll Nutr 1997;16:280–2.
26. Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: The influence of soy-based formulas. J Am Coll Nutr 1997;16:280–2.
27. Threlkeld DS, ed. Respiratory Drugs, Respiratory Inhalant Products, Anticholinergics, Ipratropium Bromide. In Facts and Comparisons Drug Information. St. Louis, MO: Facts and Comparisons, Jun 1996, 182f–2g.
28. Peng WX, Li HD, Zhou HH. Effect of daidzein on CYP1A2 activity and pharmacokinetics of theophylline in healthy volunteers. Eur J Clin Pharmacol 2003;59:237–41.
29. Divi RL, Chang HC, Doerge DR. Antithyroid isoflavones from soybean. Biochem Pharmacol 1997;54:1087–96.
30. Ishizuki Y, Hirooka Y, Murata Y, Togashi K. [The effects on the thyroid gland of soybeans administered experimentally in healthy subjects.] Nippon Naibunpi Gakkai Zasshi 1991;67:622–9. [in Japanese].
31. Forsythe WA. Soy Protein, thyroid regulation and cholesterol metabolism. Forsythe WA. Soy protein, thyroid regulation and cholesterol metabolism. J Nutr 1995;125:619S–23S.
32. Bennink MR, Mayle JE, Bourquin LD, Thiagarajan D. Evaluation of soy protein in risk reduction for colon cancer and cardiovascular disease: Preliminary results. Second International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. September 15–18, 1996. Brussels, Belgium.
33. Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: the influence of soy-based formula. J Am Coll Nutr 1997;16:280–2.
34. Messina MJ, Persky V, Setchell KD, Barnes S. Soy intake and cancer risk: a review of the in vitro and in vivo data. Nutr Cancer 1994;21:113–31.
35. Rao CV, Wang C-X, Simi B, et al. Enhancement of experimental colon cancer by genistein. Cancer Res 1997;57:3717–22.
36. Barnes S. The chemopreventive properties of soy isoflavonoids in animal models of breast cancer. Breast Cancer Res Treat 1997;46:169–79 [review].
37. Hilakivi-Clarke L, Cho E, Onojafe I, et al. Maternal exposure to genistein during pregnancy increases carcinogen-induced mammary tumorigenesis in female rat offspring. Oncol Rep 1999;6:1089–95.
38. Lu L-JW, Anderson KE, Grady JJ, Nagamani M. Effects of soya consumption for one month on steroid hormones in premenopausal women: implications for breast cancer risk reduction. Cancer Epidemiol Biomarkers Prev 1996;5:63–70.
39. Nagata C, Takatsuka N, Inaba S, et al. Effect of soymilk consumption on serum estrogen concentrations in premenopausal Japanese women. J Natl Cancer Inst 1998;90:1830–5.
40. Hargreaves DNF, Potten CS, Harding C, et al. Two-week dietary soy supplementation has an estrogenic effect on normal premenopausal breast. J Clin Endocrinol Metab 1999;84:4017–24.
41. Petrakis NL, Barnes S, King EB, et al. Stimulatory influence of soy protein isolate on breast secretion in pre- and postmenopausal women. Cancer Epidemiol Biomarkers Prev 1996;5:785–94.
42. McMichael-Phillips DF, Harding C, Morton M, et al. Effects of soy-protein supplementation on epithelial proliferation in the histologically normal human breast. Am J Clin Nutr 1998;68(suppl):1431S–6S.
43. Unfer V, Casini ML, Costabile L, et al. Endometrial effects of long-term treatment with phytoestrogens: a randomized, double-blind, placebo-controlled study. Fertil Steril 2004;82:145–8.
44. Marini H, Minutoli L, Polito F, et al. Effects of the phytoestrogen genistein on bone metabolism in osteopenic postmenopausal women: a randomized trial. Ann Intern Med 2007;146:839–47.
Last Review: 11-07-2012
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The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2013.
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