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The Benefits, Risks, and Uncertainties of Soy for Lower Blood Cholesterol
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The Benefits, Risks, and Uncertainties of Soy for Lower Blood Cholesterol

You’ve probably been seeing it for years—that white bean curd found in soups and dishes at your local Asian restaurant, that new ingredient in your power bar, that “textured vegetable protein” that your wife now mixes with your hamburger. It goes by many names—tofu, tempeh, soybeans, but it’s not just a meat-substitute for vegetarians or New-Age yuppie types. Soy-based proteins have hit the mainstream, and some evidence suggests they could be good for your heart.

Thomas Dayes is an animator in Minneapolis who turned to soy products after becoming a vegetarian. “I chose soy as a meatless alternative, but I also like the fact that it’s supposed to be good for my heart, since high cholesterol runs in my family,” he says. Dean Johnston, a financial analyst in Boston, also eats soy for its reported health benefits. “My father died of a heart attack ten years ago, and eating soy and exercising regularly are just a part of maintaining a healthy lifestyle for me.”

Researchers have examined soy's potential benefits for reducing menopausal symptoms and helping prevent cancer and osteoporosis. (As yet, there is little firm evidence that soy does any of these.) The strongest scientific evidence regards its benefits for heart health.

Soy and Cardiovascular Health

Substituting soy protein for a animal protein which is high in saturated fat will likely reduce cholesterol and may lead to lower risk of heart attack in susceptible persons. For this reason, the Food and Drug Administration (FDA) allows a “heart-healthy” label to be placed on foods containing 25 grams (g) of soy protein. This amount of soy can be found in about 2½ cups of soymilk or ½ pound of tofu. Researchers do not know the exact components of soy that lead to its health benefits. According to the combined evidence of more than 40 studies, soy appears to somewhat reduce blood cholesterol levels and to improve the ratio of LDL “bad” versus HDL “good” cholesterol.

The American Heart Association agrees that for persons currently on a high fat, high animal protein (unhealthy) diet, switching to soy may lead to some reduction in risk. However, the Association also notes that for the average person soy may offer little benefit. Even when taking in a whopping 50 g of soy protein daily, most people only see their LDL (bad) cholesterol fall by about 8%. According to the Heart Association’s 2006 “advisory,” soy has no effect on HDL (good) cholesterol or on triglycerides. Lowering LDL cholesterol by any amount may be beneficial for preventing heart disease, especially if you already have a history of heart problems or very high cholesterol levels. Despite much study, evidence doesn’t yet establish soy as a particularly powerful reducer of cholesterol or heart disease risk.

For men, the biggest benefit of soy may be on the prostate. Studies are still conflicting, but there is some evidence that diet affects prostate cancer risk, and the components of soy may reduce that risk.

Can You Have Too Much Soy?

Mr. Daye—who drinks a glass or two of soymilk and eats soy meats every day—often wonders if he’s eating too much soy. “I haven’t yet had any negative health effects from eating soy, but I do wonder if it will affect my hypothyroidism.” While the research fails to show that soy intake is especially beneficial for either the heart or other health conditions, there are some potentially worrisome effects in certain populations taking high doses of this vegetable-based protein. A 2005 book entitled The Whole Soy Story outlines many of these effects and suggests that Mr. Daye’s enthusiasm for soy may have been created more by advertising than by good science. Of particular concern is the potential effect of high doses of soy on the following:

  • Thyroid—Soy may affect the thyroid gland, but research has produced conflicting results. Soy products have been observed to reduce the absorption of thyroid medication in people with impaired thyroid function, and some evidence suggests that it may directly inhibit thyroid gland function. Other research, however, has found that soy has no effect on thyroid hormone levels, and may even increase levels. In light of soy’s potential complex effects on the thyroid, it is recommended that people with impaired thyroid function not consume large amounts of soy, except under the supervision of a physician.
  • Cancer—It is believed, but not proven, that long-term consumption of soy products reduces the risk of breast cancer. However, the ingredients in soy that are thought to protect against cancer might also stimulate breast cancer cells if they already exist. For this reason, women who have had breast cancer, or are at high risk of developing it, should probably avoid using soy until this confusing issue has been sorted out.
  • Conception and pregnancy—Soy does not appear to interfere with the action of oral contraceptives, as some have feared. However, there are theoretical concerns that a large intake of soy by a pregnant woman might exert a hormonal effect that adversely impacts the fetus.
  • Immunity—Based on very preliminary evidence, concerns have been raised that some components of soy, called isoflavones, could have a negative effect on the immune system.
  • Drug and nutrient interactions
    • Soy may reduce the absorption of calcium, iron, and zinc. For this reason, if you take a multivitamin/mineral supplement, it would be advisable to take it at least one hour before or three hours after consuming soy.
    • Individuals on thyroid medication should be aware that consuming high levels of soy may counteract these medications.

Getting More Soy Into Your Diet

Both men admit that they initially disliked the taste and texture of many soy products, but each has experimented to find soy products they like. “If the taste throws you, be patient. It takes a little time for your body and taste buds to adjust. Once they do, soy tastes great,” says Mr. Daye. You can find a multitude of soy products in your local grocery store. Some of Mr. Daye and Mr. Johnston's favorite soy products include soy ice cream, soy cheese, “power” bars containing soy, soymilk, veggie meats, and seasoned tofu.

Here are some tips on substituting soy protein for meats and other protein sources in your diet:

  • Hide it:
    • Mash a cake of tofu and use it in place of ricotta cheese in your lasagna.
    • Mix textured vegetable protein (TVP) into hamburgers and seasoned meat dishes like tacos, chili, and casseroles.
    • Add cubes of fried, seasoned tofu to salads.
  • Try Asian cuisine. Japanese, Chinese, Thai, and Vietnamese foods often contain flavorful soy options, including tofu, tempeh, and edamame (green soy beans). Edamame is eaten cold and salted. Tofu and tempeh can be stir-fried, steamed, or added to soups.
  • Use supplements and soy protein powders. Try mixing soy protein powders into smoothies or mashed potatoes.
  • Soy nuts, flavored with salt and spices, make a delicious snack.
  • Use soymilk in cereal.

Major Food Sources:

Type of ProductServing size Soy content
(grams)
Soy protein powder2 scoops, 1/3 cup18
Tempeh1/2 cup16
Soy protein bar1 bar14
Cooked/canned soybeans1/2 cup13
Dry textured soy protein concentrate usually called TVP: textured vegetable protein1/4 cup12
Soy nuts1/4 cup12
Soy burger1 patty10
Black soybeans1/2 cup9
Soy ground crumbles1/2 cup9
Water packed tofu3 ounces8.5
Dry textured soy flour (soy or vegetable protein)1/4 cup8
Plain soy milk8 ounces8
Soy nut butter2 tablespoons8
Green soybeans (edamame)1/2 cup7
Soy breakfast links2 links6.5
Soy breakfast patty1 patty6.5
Silken firm tofu3 ounces6
Vanilla soy milk8 ounces6

RESOURCES:

American College of Cardiology
http://www.acc.org/

American Heart Association
http://www.americanheart.org/

US Food and Drug Administration
http://www.fda.gov/

National Heart, Lung, and Blood Institute
http://www.nhlbi.nih.gov/

CANADIAN RESOURCES:

Canadian Council on Food and Nutrition
www.ccfn.ca

Dietitians of Canada
http://www.dietitians.ca/

Sources:

Anderson JW, Johnstone BM, Cooke-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. New Engl J of Med . 1995;333:276-281.

Harland JL, Carr TA. Does a practical daily intake of ~25 g soy protein significantly lower cholesterol?—A meta-analysis of recent studies. J of Nutr. 2004;134(5):1267S (Poster Abstract).

Indiana Soybean Board. The US Soyfoods Directory. Stevens & Associates, Inc. Indianapolis, IN; 2002.

Mackey R, Ekangaki A, Eden JA. The effects of soy protein in women and men with elevated plasma lipids. Biofactors . 2000;12:251-257.

Rosell MS, Appleby PN, Spencer EA, Key TJ. Soy intake and blood cholesterol concentrations: a cross-sectional study of 1033 pre- and postmenopausal women in the oxford arm of the European Prospective Investigation into Cancer and Nutrition. American J of Clin Nutr . 2004;80(5):1391-1396.

Hedelin M, Klint A, et al. Dietary phytoestrogen, serum enterolactone and risk of prostate cancer: the cancer prostate Sweden study (Sweden). Cancer Causes Control. Mar 2006;17(2):169-180.

Sacks FM, Lichtenstein A, Van Horn L, Harris W, Kris-Etherton P, Winston M; American Heart Association Nutrition Committee. Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation. Feb 21, 2006;113(7):1034-44.



Last reviewed June 2008 by Dianne Scheinberg MS, RD, LDN

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.


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