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Lipid Disorders and Soy

Written by ColleenO, FoundHealth.

Soy protein appears capable of modestly lowering total cholesterol, LDL ("bad") cholesterol, and triglycerides. The FDA has allowed foods containing soy protein to make the "heart-healthy" claim on the label. Substituting as little as 20 g daily of soy protein for animal protein may significantly improve cholesterol levels.

Not all soy foods and products are created equal, and soy might have some undesirable effects, such as food sensitivities and estrogenic actions. See the "How to Use Soy" and "Side Effects & Warnings" sections for more information.

Effect of Soy on Lipid Disorders

Soy contains several components that are believed to have effects on the body, including proteins, fiber, phospholipids, and isoflavones (phytoestrogens). Any or all of these elements might help reduce serum lipids. Research suggests that soy protein is especially effective for this purpose.

Read more details about Soy.

Research Evidence on Soy

Soy protein appears capable of lowering total cholesterol, LDL ("bad") cholesterol, and triglycerides by approximately 5%-15%.32,238,287 One study suggests that substituting as little as 20 g daily of soy protein for animal protein can significantly improve cholesterol levels.33 Higher doses appear to cause increased benefit.238

Although it was once thought that isoflavones are the active ingredients in soy responsible for improving cholesterol profile, evidence suggests otherwise.34-41,153,158-161,190-194,256,277,288,290 Other substances, such as certain soy proteins, may be more important. However, it has been additionally suggested that soy protein must be kept in its original state to be effective. Ordinary soy protein extracts are somewhat damaged (“denatured”), often by heat used in processing and/or cooking. In a double-blind study of 120 people, a special “preserved” soy protein extract proved more effective for improving cholesterol profile than standard denatured soy protein extracts.260

How to Use Soy

Dosage

One study suggests that substituting as little as 20 g daily of soy protein for animal protein can significantly improve cholesterol levels.33 Higher doses appear to cause increased benefit.238

Soy is increasingly added to foods in the US as a protein filler, and there are concerns that some people here may be greatly exceeding the amount of soy eaten anywhere else in the world. For comparison, in Asia, the average intake of soy is only about 10 g daily.

Sources

A number of soy foods are readily available in grocery stores and health food stores. Tofu, soy milk, and tempeh are some of the more traditional forms of soy. Soy is also used to make "cheeses," vegetarian "meat" such as veggie burgers, and other foods. Soy beans can be eaten whole in the form of edamame and roasted soy nuts.

Soy foods, especially more processed forms, can be the source of food sensitivities in some people. Soy can also be challenging to digest. Some experts recommend consuming fermented soy products, such as tempeh, because these foods are easier to digest. Some experts also recommend choosing "non GMO" soy foods because a lot of the soy cultivated today (especially in the US) is genetically modified.

As for soy supplements, it has been additionally suggested that soy protein must be kept in its original state to be effective. Ordinary soy protein extracts are somewhat damaged (“denatured”) by heat and processing. In a double-blind study of 120 people, a special “preserved” soy protein extract proved more effective for improving cholesterol profile than standard denatured soy protein extracts.260

Types of Professionals That Would Be Involved with This Treatment

  • Integrative MD
  • Naturopathic doctor
  • Nutritionist or dietitian

Safety Issues

Studies in animals have found soy essentially nontoxic. 1 And it is reassuring to note that researchers found no evidence of ill effects when they gave healthy postmenopausal women 900 mg of soy isoflavones a day for 84 consecutive days. 2 However, soy or its isoflavones could conceivably have some potentially harmful effects in certain specific situations.

Soy appears to have numerous potential effects involving the thyroid gland. When given to individuals with impaired thyroid function , soy products have been observed to reduce absorption of thyroid medication. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 In addition, some evidence hints that soy isoflavones may directly inhibit the function of the thyroid gland, although this inhibition may only be significant in individuals who are deficient in iodine. 17 However, to make matters even more confusing, studies of healthy humans and animals given soy isoflavones or other soy products have generally found that soy either had no effect on thyroid hormone levels or actually increased levels. 18 The bottom line: In view of soy’s complex effects regarding the thyroid, individuals with impaired thyroid function should not take large amounts of soy products except under the supervision of a physician.

One study found that soy products may decrease testosterone levels in men. 19 This could conceivably cause problems for men with infertility or erectile dysfunction .

Soy may reduce the absorption of the nutrients zinc, iron, and calcium. 20 21 22 23 To avoid absorption problems, you should probably take these minerals at least 2 hours apart from eating soy.

Other concerns relate to the estrogenic properties of soy isoflavones. For example, while soy is thought to reduce the risk of developing breast cancer, it is possible that soy might not be safe for women who have already had breast cancer. In addition, there are concerns that intensive use of soy products by pregnant women could exert a hormonal effect that impacts unborn fetuses. Finally, fears have been expressed by some experts that soy might interfere with the action of oral contraceptives . However, one study of 36 women found reassuring results. 24 For more information on these and other safety issues regarding the isoflavones in soy, see the full Isoflavones article.

One observational study raised concerns that soy might impair mental function. 25 However, observational studies are highly unreliable by nature, and experts do not consider this a serious issue. 26 Additionally, a number of studies looking at cognitive improvement have found that soy or soy isoflavones either have no effect on mental function, or perhaps minimally improve it. 27

Interactions You Should Know About

If you are taking:

  • Zinc , iron , or calcium supplements: It may be best to eat soy at a different time of day to avoid absorption problems.
  • Thyroid hormone : You should consult your physician before increasing your intake of soy products.

References

  1. Crowell JA, Levine BS, Page JG, et al. Preclinical safety studies of isoflavones [abstract]. J Nutr. 2000;130(suppl):677S.
  2. Pop EA, Fischer LM, Coan AD, Gitzinger M, Nakamura J, Zeisel SH. Effects of a high daily dose of soy isoflavones on DNA damage, apoptosis, and estrogenic outcomes in healthy postmenopausal women: a phase I clinical trial. Menopause. 15(4 Pt 1):684-92.
  3. Chorazy PA, Himelhoch S, Hopwood NJ, Greger NG, Postellon DC. Persistent hypothyroidism in an infant receiving a soy formula: case report and review of the literature. Pediatrics. 96(1 Pt 1):148-50.
  4. 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. 16(3):280-2.
  5. Nävert B, Sandström B, Cederblad A. Reduction of the phytate content of bran by leavening in bread and its effect on zinc absorption in man. Br J Nutr. 53(1):47-53.
  6. Hallberg L, Rossander L, Skånberg AB. Phytates and the inhibitory effect of bran on iron absorption in man. Am J Clin Nutr. 45(5):988-96.
  7. Heaney RP, Weaver CM, Fitzsimmons ML. Soybean phytate content: effect on calcium absorption. Am J Clin Nutr. 53(3):745-7.
  8. Vohra P, Gray GA, Kratzer FH. Phytic acid-metal complexes. Proc Soc Exp Biol Med. 120(2):447-9.
  9. Evans GW. Normal and abnormal zinc absorption in man and animals: the tryptophan connection. Nutr Rev. 38(4):137-41.
  10. Persky VW, Turyk ME, Wang L, Freels S, Chatterton R Jr, Barnes S, Erdman J Jr, Sepkovic DW, Bradlow HL, Potter S. Effect of soy protein on endogenous hormones in postmenopausal women. Am J Clin Nutr. 75(1):145-53.
  11. Dewell A, Hollenbeck CB, Bruce B. The effects of soy-derived phytoestrogens on serum lipids and lipoproteins in moderately hypercholesterolemic postmenopausal women. J Clin Endocrinol Metab. 87(1):118-21.
  12. Sirtori CR, Bosisio R, Pazzucconi F, et al. Soy milk with a high glycitein content does not reduce low-density lipoprotein cholesterolemia in type II hypercholesterolemic patients. Ann Nutr Metab. 2002;46:88-92.  
  13. Kotsopoulos D, Dalais FS, Liang YL, McGrath BP, Teede HJ. The effects of soy protein containing phytoestrogens on menopausal symptoms in postmenopausal women. Climacteric. 3(3):161-7.
  14. Van Patten CL, Olivotto IA, Chambers GK, Gelmon KA, Hislop TG, Templeton E, Wattie A, Prior JC. Effect of soy phytoestrogens on hot flashes in postmenopausal women with breast cancer: a randomized, controlled clinical trial. J Clin Oncol. 20(6):1449-55.
  15. Kumar NB, Cantor A, Allen K, Riccardi D, Cox CE. The specific role of isoflavones on estrogen metabolism in premenopausal women. Cancer. 94(4):1166-74.
  16. Messina M, Gardner C, Barnes S. Gaining insight into the health effects of soy but a long way still to go: commentary on the fourth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. J Nutr. 132(3):547S-551S.
  17. Doerge DR, Sheehan DM. Goitrogenic and estrogenic activity of soy isoflavones. Environ Health Perspect. 110 Suppl 3():349-53.
  18. Persky VW, Turyk ME, Wang L, Freels S, Chatterton R Jr, Barnes S, Erdman J Jr, Sepkovic DW, Bradlow HL, Potter S. Effect of soy protein on endogenous hormones in postmenopausal women. Am J Clin Nutr. 75(1):145-53.
  19. Gardner-Thorpe D, O'Hagen C, Young I, Lewis SJ. Dietary supplements of soya flour lower serum testosterone concentrations and improve markers of oxidative stress in men. Eur J Clin Nutr. 57(1):100-6.
  20. Nävert B, Sandström B, Cederblad A. Reduction of the phytate content of bran by leavening in bread and its effect on zinc absorption in man. Br J Nutr. 53(1):47-53.
  21. Hallberg L, Rossander L, Skånberg AB. Phytates and the inhibitory effect of bran on iron absorption in man. Am J Clin Nutr. 45(5):988-96.
  22. Heaney RP, Weaver CM, Fitzsimmons ML. Soybean phytate content: effect on calcium absorption. Am J Clin Nutr. 53(3):745-7.
  23. Vohra P, Gray GA, Kratzer FH. Phytic acid-metal complexes. Proc Soc Exp Biol Med. 120(2):447-9.
  24. Martini MC, Dancisak BB, Haggans CJ, Thomas W, Slavin JL. Effects of soy intake on sex hormone metabolism in premenopausal women. Nutr Cancer. 34(2):133-9.
  25. White LR, Petrovitch H, Ross GW, Masaki K, Hardman J, Nelson J, Davis D, Markesbery W. Brain aging and midlife tofu consumption. J Am Coll Nutr. 19(2):242-55.
  26. Messina M, Gardner C, Barnes S. Gaining insight into the health effects of soy but a long way still to go: commentary on the fourth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. J Nutr. 132(3):547S-551S.
  27. Kreijkamp-Kaspers S, Kok L, Grobbee DE, de Haan EH, Aleman A, Lampe JW, van der Schouw YT. Effect of soy protein containing isoflavones on cognitive function, bone mineral density, and plasma lipids in postmenopausal women: a randomized controlled trial. JAMA. 292(1):65-74.
  1. Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med. 1995;333:276-281.
  2. 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;71:1077-1084.
  3. Crouse JR III, 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;159:2070-2076.
  4. Wangen KE, Duncan AM, Xu X, et al. Soy isoflavones improve plasma lipids in normocholesterolemic and mildly hypercholesterolemic postmenopausal women. Am J Clin Nutr. 2001;73:225-231.
  5. Anthony MS, Clarkson TB, Hughes CL Jr, et al. Soybean isoflavones improve cardiovascular risk factors without affecting the reproductive system of peripubertal rhesus monkeys. J Nutr. 1996;126:43-50.
  6. Greaves KA, Parks JS, Williams JK, et al. Intact dietary soy protein, but not adding an isoflavone-rich soy extract to casein, improves plasma lipids in ovariectomized cynomolgus monkeys. J Nutr. 1999;129:1585-1592.
  7. Simons LA, von Konigsmark M, Simons J, et al. Phytoestrogens do not influence lipoprotein levels or endothelial function in healthy, postmenopausal women. Am J Cardiol. 2000;85:1297-1301.
  8. Mackey R, Ekangaki A, Eden JA. The effects of soy protein in women and men with elevated plasma lipids. Biofactors. 2000;12:251-257.
  9. Sirtori CR, Gianazza E, Manzoni C, et al. Role of isoflavones in the cholesterol reduction by soy proteins in the clinic [letter]. Am J Clin Nutr. 1997;65:166-167.
  10. Howes JB, Sullivan D, Lai N, et al. The effects of dietary supplementation with isoflavones from red clover on the lipoprotein profiles of post menopausal women with mild to moderate hypercholesterolaemia. Atherosclerosis. 2000;152:143-147.
  11. Dewell A, Hollenbeck CB, Bruce B. The effects of soy-derived phytoestrogens on serum lipids and lipoproteins in moderately hypercholesterolemic postmenopausal women. J Clin Endocrinol Metab. 2002;87:118-121.
  12. Messina M, Gardner C, Barnes S. Gaining insight into the health effects of soy but a long way still to go: commentary on the fourth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. J Nutr. 2002;132:547S-551S.
  13. Sanders TA, Dean TS, Grainger D, et al. Moderate intakes of intact soy protein rich in isoflavones compared with ethanol-extracted soy protein increase HDL but do not influence transforming growth factor beta(1) concentrations and hemostatic risk factors for coronary heart disease in healthy subjects. Am J Clin Nutr. 2002;76:373-377.
  14. 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;17:3392-3398.
  15. Jenkins DJ, Kendall CW, Jackson CJ, et al. Effects of high- and low-isoflavone soyfoods on blood lipids, oxidized LDL, homocysteine, and blood pressure in hyperlipidemic men and women. Am J Clin Nutr. 2002;76:365-372.
  16. Nikander E, Tiitinen A, Laitinen K, et al. Effects of isolated isoflavonoids on lipids, lipoproteins, insulin sensitivity, and ghrelin in postmenopausal women. J Clin Endocrinol Metab. 2004;89:3567-3572.
  17. Atkinson C, Oosthuizen W, Scollen S, et al. Modest protective effects of isoflavones from a red clover-derived dietary supplement on cardiovascular disease risk factors in perimenopausal women, and evidence of an interaction with ApoE genotype in 49-65 year-old women. J Nutr. 2004;134:1759-1764.
  18. Kreijkamp-Kaspers S, Kok L, Grobbee DE, et al. Effect of soy protein containing isoflavones on cognitive function, bone mineral density, and plasma lipids in postmenopausal women. JAMA. 2004;292:65-74.
  19. Dalais FS, Ebeling PR, Kotsopoulos D, et al. The effects of soy protein containing isoflavones on lipids and indices of bone resorption in postmenopausal women. Clin Endocrinol (Oxf). 2003;58:704-709.
  20. Yeung J, Yu TF. Effects of isoflavones (soy phyto-estrogens) on serum lipids: a meta-analysis of randomized controlled trials. Nutr J. 2003. [Epub ahead of print]
  21. Reynolds K, Chin A, Lees KA, et al. A meta-analysis of the effect of soy protein supplementation on serum lipids. Am J Cardiol. 2006;98:633-640.
  22. Ho SC, Chen YM, Ho SS, et al. Soy isoflavone supplementation and fasting serum glucose and lipid profile among postmenopausal Chinese women: A double-blind, randomized, placebo-controlled trial. Menopause. 2007 Mar 19. [Epub ahead of print]
  23. Hoie LH, Guldstrand M, Sjoholm A, et al. Cholesterol-lowering effects of a new isolated soy protein with high levels of nondenaturated protein in hypercholesterolemic patients. Adv Ther. 2007;24:439-447.
  24. Gardner CD, Messina M, Kiazand A, et al. Effect of two types of soy milk and dairy milk on plasma lipids in hypercholesterolemic adults: a randomized trial. J Am Coll Nutr. 2007;26:669-677.
  25. Harland JI, Haffner TA. Systematic review, meta-analysis and regression of randomised controlled trials reporting an association between an intake of circa 25g soya protein per day and blood cholesterol. Atherosclerosis. 2008 Apr 15.
  26. Thorp AA, Howe PR, Mori TA, et al. Soy food consumption does not lower LDL cholesterol in either equol or nonequol producers. Am J Clin Nutr. 2008;88:298-304.
  27. Rios DR, Rodrigues ET, Cardoso AP, et al. Lack of effects of isoflavones on the lipid profile of Brazilian postmenopausal women. Nutrition. 2008;24:1153-1158.

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