Hypertension and Soy

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.

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.

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

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.

• 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.

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