Transcript Soy Isoflavones - Pennington Biomedical Research Center

Soy Isoflavones
Pennington Biomedical Research Center
Division of Education
Heli J. Roy PhD
Shanna Lundy, BS
Phillip 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
Genistein
Daidzein
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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)
Soy Burger
1 patty
8
7
100
Soy nuts
1 oz
12
38
150
Soy Milk
1c
8
24
100
Texturized
Vegetable Protein
(TVP)
¼c
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
¼c
12
33
90
Soy Beans, Boiled
½c
7
47
190
Tempeh
½c
18
36
200
Soy Nut Butter
2 Tbs.
8
0
160
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Isoflavone content Kcal
(mg)
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Mechanisms of Action..
• There are many proposed mechanisms for the therapeutic
effect of isoflavones
• The mechanisms include:
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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 androgendependent and androgen-independent prostate cancer cells in
vitro
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Other Mechanisms
By 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 soyfoodconsuming 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, 7isopropoxyisoflavone, 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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Soy & Cardiovascular Health:
Plasma
lipids
lipoproteins
Plasma
Lipidsand
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”
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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
Systole
diastole
• 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
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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, soy’s roles and possibly emerging ones will be
better understood
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References…
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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