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Hypertension and Soy

Written by ColleenO, FoundHealth.

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Components of soy--including soy protein and isoflavones--may help control hypertension, though scientific evidence is mixed. Soy is rather controversial. Some experts believe it offers great health benefits, while others think it is unhelpful and even harmful for some people.

Effect of Soy on Hypertension

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 influence blood pressure.

Read more details about Soy.

Research Evidence on Soy

There is mixed evidence on whether soy protein and their associated isoflavones are helpful for blood pressure.92,102 A comprehensive review of studies investigating the influence of phytoestrogens (including soy) on blood pressure found no meaningful effect.131 However, another review found that soy protein alone could significantly reduce blood pressure.136

How to Use Soy

Dosage

Because research demonstrates that soy helps improve blood cholesterol numbers, the FDA allows soy foods containing 6-½ grams of soy to carry a heart-healthy label. Evidence suggests that a daily intake of 25 g of soy protein is adequate to noticeably reduce cholesterol. This amount is typically found in about 2-½ cups of soy milk or ½ pound of tofu.

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. Even the 25 g amount recommended for reducing cholesterol levels is relatively high. 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.

Types of Professionals That Would Be Involved with This Treatment

  • Nutritionist or dietitian
  • Naturopathic doctor
  • Integrative MD

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. 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.
  2. Teede HJ, Giannopoulos D, Dalais FS, et al. Randomised, controlled, cross-over trial of soy protein with isoflavones on blood pressure and arterial function in hypertensive subjects. J Am Coll Nutr. 2006;25:533-540.
  3. Rosero Arenas MA, Rosero Arenas E, Portaceli Arminana MA, et al. Usefulness of phyto-oestrogens in reduction of blood pressure. Systematic review and meta-analysis. Aten Primaria. 2008;40:177-186.
  4. Hooper L, Kroon PA, Rimm EB, et al. Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2008;88:38-50.

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