PBRC 2005 1

Soy Isoflavones

Pennington Biomedical Research Center

Division of EducationHeli J. Roy PhD

Shanna Lundy, BSPhillip Brantley, PhD, Director

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General info…

• Soy is a low cost source of protein that has been consumed in Asian nations for many centuries

• Regular intake of this food is thought to be partially responsible for the lower rates of heart disease, stroke, and cancer observed in Eastern populations.

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• Isoflavones are members of the large flavonoid family of plant compounds which are, in turn, members of the larger group of plant constituents known as polyphenols

• The principal isoflavones in soy are genistein, daidzein, and their metabolites

DaidzeinGenistein

Information..

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Good sources of Soy…• Edamame or Soy beans: Soy beans are the least processed form of soy protein. They are available in

most grocery stores and can be purchased in fresh, frozen, or roasted forms

• Tofu: Tofu, or bean curd, is made my curdling soymilk with a coagulant. Tofu can

be used in a variety of recipes to partially replace either meat or dairy products. Because calcium sulfate is often used as the curdling agent, tofu is also a good source of calcium.

• Soymilk: Soymilk is a high-quality source of soy protein that’s available in a variety of

forms, including chocolate.

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Sources…

• Isoflavone compounds, such as genistein and daidzein, are found in a number of plants, but soybeans and soy products like tofu and textured vegetable protein are the primary food sources.

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Food Serving

Soy protein (g)

Isoflavone content (mg)

Kcal

Soy Burger 1 patty 8 7 100

Soy nuts 1 oz 12 38 150

Soy Milk 1 c 8 24 100

Texturized Vegetable Protein

(TVP)

¼ c 14 27 50

Tofu 3 oz 9 33 45

Soy Protein Bar 1 bar 6 10-15 180

Soy Breakfast Patty

2 patties 16 4 160

Soy Flour ¼ c 12 33 90

Soy Beans, Boiled ½ c 7 47 190

Tempeh ½ c 18 36 200

Soy Nut Butter 2 Tbs. 8 0 160

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• There are many proposed mechanisms for the therapeutic effect of isoflavones

• The mechanisms include:– binding to estrogen receptors– inhibition of production of reactive oxygen species– induction of DNA strand breakage resulting in apoptosis or cell death– inhibition of angiogenesis– inhibition of thrombin formation and platelet activation– And increased LDL receptor activity

Mechanisms of Action..

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Health Effects of Soy

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• Relative to physiologic estrogens, isoflavones appear to be a weaker form according to both in vitro and in vivo assays

• Because of this, its believed that isoflavones can compete at estrogen receptor sites, blocking the stronger version naturally produced by the body from exerting its full effect

• Since high blood levels of estrogen are an established risk factor for breast cancer, weaker forms of estrogen may provide protection against this disease

Estrogenic and Antiestrogenic Activity

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• The prevailing hypothesis has been that isoflavones exert antiestrogenic effects when placed in a high-estrogen environment, such as exists in premenopausal women, and estrogenic effects when in a low-estrogen environment, such as exists in postmenopausal women

• There has been some support to this hypothesis, however definite conclusions regarding whether soy or isoflavones are necessarily antiestrogenic in premenopausal women is still currently a topic of much debate

Estrogenic and Antiestrogenic Activity

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• Interest in the relationship between soy intake and cancer risk was due, in large part, to the relatively low breast cancer mortality rates in Asian countries where soyfoods are commonly consumed

• In Japan, the breast cancer mortality rate is about ¼ that of the United States

Breast Cancer

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• Of the multitude of studies conducted outside the US on women, most find that there are decreases in breast cancer risk with consumption of soy products in premenopausal, but not postmenopausal women

• The only case-controlled study conducted thus far in the United States to examine this possible relationship found that tofu consumption was protective in both premenopausal and postmenopausal Asian women

• The downfall of this study was that it only included one particular group of women- whether or not this would be indicative of other women remains unseen

Breast Cancer

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• Overall, the epidemiologic data are inconclusive

• There is little epidemiologic support for the notion that soy intake is associated with a decreased risk of postmenopausal breast cancer

• However, there is some data suggestive of decreased risk of premenopausal breast cancer with increased soy intakes

Breast Cancer

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• There is speculation that the intake of soyfoods may be a factor contributing to the low prostate cancer mortality rate in Japan

• Although the data in support of this hypothesis is intriguing, it is also limiting

• Genistein has shown to inhibit the growth of both androgen-dependent and androgen-independent prostate cancer cells in vitro

Prostate Cancer

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• Even though the precise role of estrogen in prostate cancer is not well defined, the potential estrogenic effects of isoflavones may be protective because estrogens have been used successfully as a form of hormone therapy for metastatic prostate cancer

Other MechanismsBy which genistein or isoflavones could reduce prostate cancer risk

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• Human data available remains limited for use in evaluating the soy-prostate cancer hypothesis

• Of potential relevance to the effects of isoflavones on prostate cancer risk is the finding that isoflavones appear in the prostatic fluid, and that concentrations are highest in men from soyfood-consuming countries

• Furthermore, relative to plasma concentrations, isoflavones are concentrated several-fold in the prostatic fluid

Prostate Cancer

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• Speculation about the potential benefits of isoflavones was in part fueled by the similarity in chemical structure between the soybean isoflavones and the synthetic isoflavone, 7-isopropoxyisoflavone, which was shown to increase bone mass in postmenopausal women

Soy and Bone Health

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• Two human studies that examined the effects of soy consumption on bone mineral loss in postmenopausal women have been reported thus far

• In both studies, soy was associated with favorable effects on bone density or content; however, the results are still considered preliminary

Soy and Bone Health

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• Although the effects of soy and isoflavones on bone health constitutes and exciting area of research, no firm conclusions can be reached at this time

• With the large number of studies currently underway in this area; however, a better understanding should be on its way soon

Soy & Bone Health

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• Dietary soy protein has been shown to have several beneficial effects on cardiovascular health

• Best-documented effect is on plasma lipid and lipoprotein concentrations, with reductions of ~10% in LDL cholesterol and small increases in HDL cholesterol

• Dietary soy protein improves flow-mediated arterial dilation

• Soy isoflavone extracts improves systemic arterial compliance, an indicator of atherosclerosis extent

Soy & Cardiovascular Health: An Overview

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Plasma lipids and lipoproteins

• Effects of dietary soy protein in human subjects has shown reductions in LDL cholesterol of ~13%, reductions in plasma triglycerides of ~10%, and increases in HDL cholesterol of around 2%

• These beneficial effects of soy protein on plasma lipoproteins culminated recently in the U.S. Food and Drug Administration’s approval of the health claim that:– “25 g of soy protein a day, as part of a diet low in saturated fat

and cholesterol, may reduce the risk of heart disease”

Soy & Cardiovascular Health: Plasma Lipids and

Lipoproteins

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• Interest is increasing in the role of LDL particle oxidation on both atherogenesis and vascular function

• In healthy subjects receiving supplementation, soy treatment significantly prolonged LDL oxidation by ~20 minutes

• Based on the findings that estradiol fatty esters were incorporated into LDL, Helisten et al. described that because soy isoflavones are incorporated into LDL particles, it results in much greater oxidation resistance

Soy & Cardiovascular Health: LDL Oxidation

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Endothelium-mediated vasodilation

• Two approaches are used to evaluate endothelium-mediated vasodilation

– One determines the response of arteries to the perfusion of acetylcholine

– The other is flow-mediated dilation whereby flow is restricted

• When genistein was infused it resulted in increased brachial artery dilation of both men and women comparable to the effect of estradiol

Soy & Cardiovascular Health: Arterial Function

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Arterial Compliance

• Unlike endothelial-mediated vasodilation (primarily nitric oxide dependent), arterial compliance relates to the constriction and dilation of arteries associated with systole and diastole

• In humans, supplementation with soy protein or the administration of isoflavone extracts seems to improve arterial compliance

Soy & Cardiovascular Health: Arterial Function

Systole diastole

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• Currently, there is considerable literature establishing that substitution of animal protein (usually casein) with soy protein results in reduced amounts of atherosclerosis resulting from diets with added cholesterol

• Current research is focusing primarily on identifying what components of soy protein provide this atherosclerosis protection

Soy & Cardiovascular Health: Atherosclerosis

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• Intact soy protein provides more cardiovascular benefits than does alcohol-washed soy protein

• The addition of soy isoflavone extracts to diets containing animal protein or alcohol-washed soy protein does not provide plasma lipid concentration benefits

• Lastly, soy isoflavone extracts given to human subjects do not result in cardiovascular benefits except for improvements in systemic arterial compliance

Soy & Cardiovascular Health Atherosclerosis:

Conclusions

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• Dietary soy intake seems to be promising in the areas of cardiovascular, cancer (especially prostate), and bone health

• In time, soy’s roles and possibly emerging ones will be better understood

Conclusions…

• http://nutrition.ucdavis.edu/infosheets/soy.htm • http://www.ajcn.org/cgi/content/full/70/3/439S • http://www.nutrition.org/cgi/content/full/132/3/566S • http://www.fwhc.org/health/soy.htm • http://www3.cancer.gov/prevention/agents/Soy_Isoflavones.html• http://www.thorne.com/altmedrev/.fulltext/3/5/376.pdf

References…