Soy Isoflavones

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Soy Isoflavones

• Pennington Biomedical Research Center
• Division of Education
• Heli J. Roy PhDShanna 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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Information..

• 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

Daidzein
Genistein
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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 thats 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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Mechanisms of Action..

• 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

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Health Effects of Soy
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Estrogenic and Antiestrogenic Activity

• 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

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Estrogenic and Antiestrogenic Activity

• 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

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Breast Cancer

• 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

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Breast Cancer

• 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

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Breast Cancer

• 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

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Prostate Cancer

• 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

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Other MechanismsBy which genistein or
isoflavones could reduce
prostate cancer risk

• 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

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Prostate Cancer

• 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

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Soy and Bone Health

• 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

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Soy and Bone Health

• 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

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Soy Bone Health

• 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

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Soy Cardiovascular Health An Overview

• 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

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Plasma lipids and lipoproteins
Soy Cardiovascular Health 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 Administrations 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

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Soy Cardiovascular Health LDL
Oxidation

• 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

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Soy Cardiovascular Health Arterial
Function

• 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

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Soy Cardiovascular Health Arterial
Function

• 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

Systole diastole
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Soy Cardiovascular Health
Atherosclerosis

• 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

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Soy Cardiovascular Health
Atherosclerosis Conclusions

• 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

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Conclusions

• Dietary soy intake seems to be promising in the
  areas of cardiovascular, cancer (especially
  prostate), and bone health
• In time, soys roles and possibly emerging ones
  will be better understood

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References

• http//nutrition.ucdavis.edu/infosheets/soy.htm
• http//www.ajcn.org/cgi/content/full/70/3/439S
• http//www.nutrition.org/cgi/content/full/132/3/56
  6S
• http//www.fwhc.org/health/soy.htm
• http//www3.cancer.gov/prevention/agents/Soy_Isofl
  avones.html
• http//www.thorne.com/altmedrev/.fulltext/3/5/376.
  pdf