1
Soyfoods are a unique dietary source of isoflavones,
a phytoestrogen that may offer women heart health
benefits and may help alleviate hot flashes during
menopause.
Soyfoods offer health benefits for all
consumers, but studies show that
postmenopausal women may reap
particular benefits. This factsheet
discusses recent research into the benefits
and safety of soy for women, from heart
disease to hot flashes.
Traditional soyfoods such as tofu and miso have been widely used in
many East Asian countries for centuries and have been consumed by
health-conscious individuals in Western countries for several decades. In
recent years, because of the purported health benefits, increased numbers
of Westerners have decided to incorporate soy into their diets. Soyfoods
hold particular appeal for postmenopausal women because they are such
uniquely rich sources of isoflavones, one type of phytoestrogen.
Isoflavones exhibit estrogen-like effects under certain experimental
conditions and are posited to reduce the risk of coronary heart disease,
1
osteoporosis,
2
certain forms of cancer
3
and may alleviate menopause-
related hot flashes.
4
Consequently, many women view soyfoods as natural
alternatives to conventional hormone therapy. Women who use alternative
therapies express a desire to have control over their symptoms and the
way in which their menopause is treated.
5
Not surprisingly, interest in
alternative therapies increased following the publication of results of the
Women’s Health Initiative (WHI) trial in 2002, which showed that the risk
of long-term use of combined hormone therapy (estrogen plus progestin)
outweighed the benefits.
6
In 2010, 11-year follow up data from the WHI trial
found not only that combined hormone therapy increases breast cancer
risk but also breast cancer mortality.
7
However, isoflavones themselves are not without controversy. Their
estrogen-like effects have raised concern that these soybean constituents
possess some of the same undesirable properties as hormone therapy. In
particular, there is controversy over whether soyfoods are contraindicated
for women who have breast cancer or who are at high risk of developing
breast cancer.
8
Overview of Isoflavones
Isoflavones have a limited distribution in nature. In fact, diets that do not
include soyfoods are almost devoid of these compounds.
9
Not surprisingly,
whereas average isoflavone intake among adults ranges from about
30-50 mg/day in Japan and Chinese cities such as Shanghai,
10
intake is less
than 3 mg/day in theUnited States and other Western countries.
11, 12, 14-17
Using weighted, 2-day food consumption data for the U.S. population from
the National Health and Nutrition Examination Survey (NHANES) 2007-
2008, theUnited States Department of Agriculture recently estimated that
daily per capita isoflavone intake is 0.68 mg/day.
18
Isoflavones occur in soybeans as glycosides (a sugar molecule is attached
to the isoflavone backbone);
19
upon ingestion, the sugar is hydrolyzed
thereby allowing absorption to occur.
20
In fermented soyfoods such as
miso, tempeh and natto, substantial amounts of the isoflavones occur as
aglycones due to bacterial hydrolysis. The three isoflavones genistein,
daidzein and glycitein and their respective glycosides account for
approximately 50 percent, 40 percent and 10 percent, respectively, of the
total isoflavone content of soybeans.
19
Each gram of soy protein in soybeans and traditional soyfoods is
associated with approximately 3.5 mg of isoflavones.
10
In this document,
isoflavone amounts are expressed in aglycone equivalent weights.
Consequently, one serving of a traditional soyfood, such as 3-4 oz of tofu
or 1 cup of soymilk, typically provides about 25 mg of isoflavones.
Soy protein is present in a wide range of commonly consumed foods in the
U.S. However, isoflavone exposure from these foods is almost negligible
for two reasons. First, the amount of soy protein in these foods is quite
small because it is added for functional (not nutritional) purposes such as
bleaching, moisture retention, oxidation inhibition and improved texture.
And second, the isoflavone concentration of thesoy protein used in this
way is generally quite low in comparison to traditional soyfoods. The
isoflavone-to-protein ratio noted above for traditional soyfoods does not
apply to many processed forms of soy.
Soy
WOMEN
Soy connectionfact Sheet
by theunitedSoybean board
2
In most clinical trials, hot flash relief is achieved by
ingesting approximately 50 mg total isoflavones daily.
Soyfoods are unique because they are rich dietary
sources of isoflavones, which are endocrine
active substances but different from the hormone
estrogen.
Isoflavones are diphenolic compounds with a chemical structure similar
to the hormone estrogen; they bind to both estrogen receptors alpha and
beta – ERα and ERβ.
21, 22
For this reason, they are commonly referred to as
phytoestrogens. Their relative binding affinity is lower than that of estrogen
(17β-estradiol), but circulating levels of isoflavones in people consuming
soyfoods are approximately three orders of magnitude higher than levels of
estrogen.
23
While estrogen binds to and transactivates both ERα and ERβ
equally, isoflavones preferentially bind to and transactivate ERβ.
24-27
This
difference in binding and transactivation between isoflavones and estrogen
is important because the two estrogen receptors have different tissue
distributions and, when activated, can have different and sometimes even
opposite physiological effects. This appears to be the case in the breast,
where ERβ transactivation is thought to inhibit the proliferative effects of
ERα transactivation.
28, 29
The preference of isoflavones for ERβ is one reason they exert tissue-
selective effects, and for this reason, isoflavones are classified as selective
estrogen receptor modulators (SERMs).
30-32
In tissues that possess
estrogen receptors, SERMs exert estrogen-like effects in some cases
but no effects or antiestrogenic effects in others. The pharmaceutical
industry has for many years been actively developing SERMs.
33
Widely
used SERMs include tamoxifen, used in breast cancer treatment, and
raloxifene, which is used for treatment of osteoporosis.
34
In addition to
being classified as phytoestrogens and SERMs, the European Food Safety
Authority has recently proposed a new classification for compounds such
as isoflavones, which is “endocrine active substances.”
35
From the above discussion, it is clear that isoflavones should not be
equated with the hormone estrogen. The clinical literature is replete with
examples of differences between these two molecules.
32, 36-56
Furthermore,
isoflavones may exert potentially-relevant hormone-independent
physiological effects. Therefore, the classification related to their hormonal
activity may be an incomplete characterization.
57
Finally, not only should
isoflavones not be equated with estrogen but soyfoods should not be
equated with isoflavones. This is because the soybean, like all foods, is a
collection of hundreds of biologically active molecules.
58
Soy, Isoflavones and Hot Flashes
Hot flashes are the most common reason given by women seeking
treatment for menopausal symptoms. For the majority of women who
experience them, hot flashes begin prior to menopause. Ten to 15 percent
of these women experience hot flashes that are severe and frequent.
59
Although hot flashes usually subside after six months to two years,
59, 60
many women report having them for up to 20 years after menopause.
61
The etiology of hot flashes is not fully understood but the drop in
circulating estrogen levels that occurs during menopause is recognized
as one factor. The low incidence of hot flashes in Japan gave rise to initial
speculation that isoflavones could be useful in their prevention.
62
Even Chinese-American and Japanese-American women are about
one-third less likely to report experiencing hot flashes than Caucasian
women.
63
Interestingly, among Asian women, chilliness and shoulder
aches are much more commonly reported menopausal symptoms than
hot flashes. Recent evidence suggests, however, that Japanese women are
reluctant to report having hot flashes.
64
To this point, one study found that
hot flash frequency was lower among Japanese compared to Caucasian
women when based on a subjective determination (personal diary), but
not when determined objectively by measuring sternal and nuchal skin
conductance.
65
Sources of Soy Protein
Soyfood Serving size
Grams of
soy protein
Fortified soymilk 1 cup 6-7
Soy cereal
1 ¼ cup 7
Soy yogurt, vanilla
1 cup 6
Soy breakfast patty
2 patties 11
Soy bar
1 bar 14
Soy chips
1 bag 7
Soynut butter
2 Tbsp 7
Soynuts, roasted, unsalted
¼ cup 11
Tofu
½ cup 10
Edamame
½ cup 11
Soy burger
1 patty 13-14
Soy pasta
½ cup (cooked) 13
Soy pudding
½ cup
6
3
isoflavones is consistent with the degree of benefit deemed satisfactory by
women seeking non-hormonal treatments for hot flashes.
76
The amount
of isoflavones providing symptom relief is found in approximately two
servings of traditional soyfoods.
Osteoporosis
In response to declining estrogen levels, women can lose substantial
amounts of bone mass in the decade following menopause, which markedly
increases their fracture risk.
77
Estrogen therapy reduces postmenopausal
bone loss and hip fracture risk by approximately one-third.
6
Recent data
shows that the protective effects against hip fracture are lost within two
years of cessation of estrogen therapy.
78
Initial speculation that soyfoods
might promote bone health in postmenopausal women was based on the
estrogen-like effects of isoflavones and early research showing that the
synthetic isoflavone, ipriflavone, exerted skeletal benefits.
79
Since 1995, more than 50 clinical trials have examined the impact of
isoflavone-rich soyfoods or isoflavone supplements on the alleviation
of menopause-related hot flashes. In recent years, investigators have
gravitated toward the use of supplements rather than soyfoods to enhance
compliance and reduce the complexity of study design. The results of
these trials have produced inconsistent results. Although some recent
reviews and analyses of the literature have concluded that isoflavone-rich
products alleviate hot flashes,
4, 66
most have found that the data does not
allow for definitive conclusions to be made even though more trials than
not showed benefit.
67, 68
Some inconsistency in the literature is expected
given the small sample size of many trials and the variable placebo
response. However, several more specific explanations for the seemingly
inconsistent data have been proposed, including intraindividual differences
in isoflavone metabolism,
69
differences in baseline hot flash frequency (i.e.,
isoflavones are more effective in women with more frequent hot flashes)
66
and differences in the isoflavone content or profile of the intervention
products (i.e., products containing higher amounts of genistein are
deemed to be most effective).
70
In response to the ingestion of the same amount of isoflavones, serum
levels of isoflavones and their metabolites differ by a factor of several
hundred among individuals.
20, 71
Therefore, it is reasonable to speculate
that differences in metabolism can affect the response to soyfoods, at
least for health outcomes thought to be affected by isoflavones. However,
this explanation appears to be more applicable to differences between
individual women’s experiences and less likely to explain why large-scale
studies would report variable outcomes. In contrast, differences in the
isoflavone content of the intervention products appear more applicable
to differences in results among studies. Some of the inconsistency may
also be because the two main soy-derived isoflavone supplements that
are available commercially and that have been used in the clinical trials
have markedly different isoflavone profiles.
72
One is high in genistein and
daidzein but low in glycitein, which is similar to the isoflavone profile of
soyfoods, whereas the other is very low in genistein and high in daidzein
and glycitein. Several lines of evidence, including relative estrogen
receptor binding and transactivation, indicate that genistein is more potent
than daidzein or glycitein and there is evidence that genistein is more
potent than the other isoflavones for alleviating hot flashes.
73, 74
The most comprehensive statistical analysis of the literature, which was
only recently published, clearly supports the efficacy of isoflavones
for alleviating hot flashes.
75
This systematic review and meta-analysis
included 19 and 17 studies, respectively, and included only studies
involving isoflavone supplements derived from soy. The meta-analysis of
the data on hot flash frequency, which included 13 studies involving 1,196
women, found isoflavones were consistently efficacious, reducing the
number of hot flashes per day about 21 percent more than the reduction
in the placebo group. Similarly, in the nine trials involving 988 women
that evaluated hot flash severity, isoflavones reduced symptoms by
about 26 percent more than the reduction in the placebo group. For both
measures, the effect of isoflavones was highly statistically significant.
When considering the combined effect of the placebo and isoflavones,
the overall reduction in frequency and severity was approximately 50
percent. Furthermore, subanalysis indicated that isoflavone supplements
providing at least 18 mg genistein were more than twice as efficacious
as supplements lower in genistein. As noted previously, genistein is the
predominant isoflavone in soybeans.
Collectively, this data makes a convincing case that isoflavones can be of
help to women who experience hot flashes. The level of relief provided by
The relatively low hip-fracture rates in Asian countries have also been cited
as evidence for the skeletal benefits of isoflavones, but other factors may
help explain these rates.
80
For example, Asians have a shorter hip axis
length, which reduces risk for fracture.
81, 82
Also, Japanese women are less
likely than Western women to fall, the precipitating event for hip fracture.
83, 84
However, spinal bone mineral density (BMD) and spinal fracture rates are
similar between Asians and Caucasians.
85-92
Nevertheless, the available
evidence shows that, among Chinese women, high soy consumers are less
likely to report having a fracture.
Fortified soymilk is a good source of isoflavones
and also contains calcium, vitamin D and protein,
which offer additional bone health benefits.
4
Two prospective epidemiologic studies have evaluated the relationship
between soy intake and fracture risk. In both, risk was reduced by
approximately one-third when women in the highest soy intake quintile or
quartile were compared to women in the lowest. This degree of protection
is similar to that noted for estrogen therapy.
6
In one of the prospective
studies, approximately 1,800 fractures of all types occurred in the 24,000
postmenopausal Shanghai women who were followed for 4.5 years.
93
In the
other, there were almost 700 hip fractures (the only site studied) among the
35,000 postmenopausal Singaporean women during the 7-year follow up
period.
94
In a third prospective epidemiologic study involving Seventh-day
Adventists, a religious denomination that includes a high proportion
of vegetarians, soymilk intake was significantly inversely related to
osteoporosis.
95
In this study, which involved 337 postmenopausal women,
participants had their bone health assessed using broadband ultrasound
attenuation of the calcaneus two years after completing a lifestyle and
dietary questionnaire at enrollment. Compared with women who did not
drink soymilk, women drinking soymilk once a day or more had 56 percent
lower odds of osteoporosis (defined as defined as a T-score <-1.8).
However, the protective effect of soymilk was likely due to its calcium
rather than isoflavone content since dairy product intake was similarly
protective. Although the results of these three studies are intriguing,
definitive conclusions about the skeletal effects of soyfoods can only be
based on the results from appropriately designed clinical studies.
Since the first clinical study to examine the effects of an isoflavone-rich
product on bone mineral density (BMD) in postmenopausal women was
published in 1998,
96
more than 25 trials have provided results (for reviews,
see references) although many involved small numbers of subjects and
were conducted for relatively short durations.
97, 9 8
Ideally, studies of bone
health should be at least 2-3 years in duration. The results from the clinical
research thus far has been mixed, as recently published meta-analyses of
the data concluded that isoflavones reduce bone breakdown
99
and increase
both bone formation
99
and spinal BMD
2, 100
in postmenopausal women.
However, a more rigorously-conducted meta-analysis failed to provide
support for the skeletal benefits of isoflavones.
101
Among the many clinical trials, one of the longest (two years) and largest
(304 subjects) published to date found that postmenopausal Italian
women with osteopenia who were assigned to the placebo group lost
approximately 6 percent of their BMD at the spine and hip, whereas those
women in the genistein group (54 mg/day genistein aglycone provided
as a supplement) gained approximately this much bone at both skeletal
sites.
54
Although intended to last only two years, approximately half of
the subjects agreed to continue for a third year; the differences between
groups in the third year were even more striking.
102
However, these results stand in stark contrast to several recently
conducted trials. For example, a 1-year study involving women from three
European countries failed to show that isoflavone supplements (110 mg/
day) inhibited bone loss in early postmenopausal women.
103
In agreement,
another 1-year trial failed to show that either isoflavone supplements or
isoflavone-rich soy protein affected bone loss in U.S. postmenopausal
women.
104
Similarly, a recently published 2-year study found that soy
protein, regardless of isoflavone content, failed to prevent bone loss in
postmenopausal women, although this study had a large dropout rate and
many women were non-compliant with the intervention.
105
According to the American Cancer Society, breast
cancer patients can consume up to 3 servings of
soyfoods daily.
Lastly, the most important results were from three very large studies, two of
which were two years
106, 107
in duration whereas the third was three years in
duration.
108
Two of these were conducted in the U.S.
106, 107
and one in Taiwan.
108
Isoflavone intake from supplements was 80 and 120 mg/day in one study,
109
200 mg/day in another
107
and 300 mg/day in the third.
108
The results from
these trials provide no support for the skeletal benefits of isoflavones
and they agree with those from a trial that utilized a novel methodology
to examine the effects of estrogen and a variety of phytoestrogen
supplements on bone reabsorption. Only at very high doses – doses
exceeding typical isoflavone exposure from soyfoods – was there any
evidence of antiresorptive effects.
73
It is unclear why the previously mentioned Italian study
102
found such
protective effects of genistein, in contrast to other studies using mixed
isoflavones that would have provided similar amounts of genistein. Also
unclear is why the two Chinese prospective epidemiologic studies found
soy intake was so protective against fracture. It is possible that those
subjects who consumed soyfoods also led an overall healthier lifestyle (the
“healthy user effect”). Yet, since soyfoods are traditional foods in Asian
countries, this is less likely to be the explanation than it would be in non-
5
At study termination, progression among the women consuming soy was
16 percent lower than in the milk group. While the difference was not
statistically significant, the results are intriguing. If a 16 percent decrease
in the progression of CIMT translates into a 16 percent decrease in the
risk of future coronary events, the public health implications would be
dramatic. Furthermore, the difference between groups increased steadily
over the 3-year study period. This suggests that after a longer period of
soy exposure, progression would have been reduced to an even greater
extent, and with it, risk of coronary events.
Additionally, subanalysis of the results revealed that among women
who were fewer than 5 years, 5-10 years, and more than 10 years post-
menopause, CIMT progression was reduced by 68 (p=0.05), 17 (p=0.51)
and 9 percent (p=0.77), respectively. It is notable that progression was
reduced so significantly in early postmenopausal women for two reasons.
First, it adds substantially to the biological plausibility of the findings, and
second, it provides clear insight into thesoy component responsible for
the beneficial effects. The pronounced effect in early menopausal women
suggests isoflavones were primarily responsible for the reduced CIMT
progression. Over the past 10 years, a hypothesis has emerged, referred
to as the “estrogen timing hypothesis.” This maintains that exposure to
estrogen-like compounds leads to dramatic coronary and cognitive benefits
when begun soon after menopause, but has less effect in later years.
125
Asian countries where soyfoods are generally perceived as health foods.
Another explanation is that in the epidemiologic studies, isoflavone intake
occurred via the consumption of traditional soyfoods, whereas the clinical
studies have generally used soy extracts. However, there is no evidence
that this difference matters with respect to skeletal effects. It may also
be that the effects noted in the epidemiologic studies result from lifelong
intake as opposed to the relatively short-term intervention periods begun
in adulthood in the clinical studies. At the same time, there is no direct
evidence supporting this suggestion.
At this point, the evidence that isoflavones provide skeletal benefits is
unimpressive. Soyfoods have other benefits in this regard, however, since
they provide high quality protein,
110
which may promote bone health.
111, 112
In addition, some are good sources of calcium as well as vitamin D.
113
Importantly, the absorption of calcium from calcium-set tofu
114
and
calcium-fortified soymilk
113, 115
is comparable to the absorption of this
mineral from cow’s milk.
Heart Health
Soyfoods potentially offer protection against heart disease through
several different mechanisms. Soyfoods are low in saturated and high
in polyunsaturated fat.
116
In addition, soy protein directly lowers blood
cholesterol levels, an attribute that was formally recognized bythe U.S.
Food and Drug Administration in 1999.
117
Estimates are that, via the fatty
acid profile and soy protein content, when soyfoods replace conventional
sources of protein in Western diets, blood low-density-lipoprotein (LDL)
cholesterol levels will be lowered by about 8 percent. In theory, over a
period of years, this may reduce risk of coronary heart disease (CHD) by
8-16 percent.
118
There is also evidence that, independent of effects on blood cholesterol,
soyfoods may reduce CHD risk. For example, four recently published
meta-analyses found that soy lowered blood pressure.
119-122
Furthermore,
isoflavones improve impaired endothelial function in postmenopausal
women.
123
Lastly, the most important study came from the Women’s
Isoflavone Soy Health (WISH). This 3-year study involved 350 healthy
postmenopausal women ages 45-92, and found that isoflavone-rich soy
protein inhibited the progression of subclinical atherosclerosis.
124
Subclinical atherosclerosis can be assessed using ultrasound to measure
the thickness of the carotid arteries—which are located on both sides
of the neck beneath the jawline and provide the main blood supply to the
brain. The thickness of the carotid artery is referred to as carotid intima-
media thickness or CIMT. Typically, CIMT increases or progresses over
time; the extent of progression reflects risk of future coronary events.
Participants in the WISH study were randomly assigned to groups
consuming either 25 g of isolated soy protein per day or 25g of milk
protein. Thesoy protein provided 99 mg of isoflavones (expressed in
aglycone equivalent weight).
Soyfoods may offer protection against heart
disease, as they are low in saturated fat and high in
polyunsaturated fats.
6
Breast Cancer
There has been rigorous investigation of the role of soyfoods in
reducing breast cancer risk. A recent meta-analysis found that, in Asian
epidemiologic studies, higher soy intake was associated with a 29
percent decreased risk of breast cancer.
3
However, there is solid evidence
indicating that to derive this benefit, soy consumption must occur during
childhood or adolescence.
126-128
In animal studies, when very young
rodents are exposed to isoflavones, breast or mammary cells undergo a
change that makes them permanently less likely to be transformed into
cancer cells later in life.
126, 129-131
This proposed mechanism may be similar
to that proposed for the protective effect of early pregnancy against breast
cancer.
132
Despite the proposed benefits, the relationship between soyfoods and
breast cancer is controversial due to concern, based almost exclusively on
in vitro and rodent data, that isoflavones may be contraindicated for women
with breast cancer or who are at high risk of developing breast cancer.
133
The position of the American Cancer Society is that women with breast
cancer can safely consume up to three servings of traditional soyfoods
daily.
134
However, their review of this issue was rather brief and was
conducted prior to the publication of important clinical and epidemiologic
data. A review of the breast cancer controversy is presented below.
At high concentrations, the isoflavone genistein inhibits the growth of
estrogen-sensitive breast cancer cells in vitro, whereas at lower, more
physiologic concentrations, growth is stimulated.
135
More importantly,
isoflavone-containing products have been found to stimulate the growth
of mammary tumors in ovariectomized athymic mice implanted with
estrogen-sensitive breast cancer cells.
136
Stimulation appears to result
primarily from exposure to the isoflavone genistein.
137
In this model,
genistein was also found to inhibit the efficacy of tamoxifen and the
aromatase inhibitor, letrozole.
138
Interestingly, more highly processed soy
products stimulate tumor growth to a greater extent than less processed
ones, despite containing similar amounts of genistein.
139
In fact, soy flour,
the least processed product to be evaluated, does not result in tumor
stimulation.
However, the relevance of this processing effect is in question because
it has now been established that, in athymic mice, processing affects
genistein pharmacokinetics in a way that leads to greater tumor
stimulation, which is not the case in humans.
140, 141
Also, Japanese
researchers, using the previously described mouse model, found that
genistein did not stimulate tumors.
142
Prior to implantation, the cancer cells
were cultured in estrogen-free media, whereas in the model which found
that genistein stimulated tumors, cells were cultured in media containing
a high concentration of estrogen. The Japanese researchers maintain that
the latter is unphysiologic and makes the cells hypersensitive to estrogenic
molecules. Clearly, there are limitations to animal research and resolving
the soy and breast cancer controversy will require human data.
The pertinent human data suggest that isoflavones do not exert stimulatory
effects on breast tissue. Isoflavones do not increase breast tissue density
or breast cell proliferation in vivo, both of which are markers of breast
cancer risk.
143
In contrast, combined menopausal hormone therapy, which
increases breast cancer risk, increases breast cell proliferation four-fold
within just 12 weeks.
144, 145
Thus, the clinical data are supportive of safety,
but the lack of effects in these studies also argues that adult soy intake
does not reduce breast cancer risk at this point in life.
The lack of harmful effects noted in the clinical studies are consistent
with the results from four prospective epidemiologic investigations. They
examined the impact of post-diagnosis soyfood intake on the prognosis
in women who have had breast cancer. The first study was designed to
specifically examine thesoy and breast cancer controversy. Data from the
Shanghai Breast Cancer Survival Study (SBCSS),
146
a population-based
cohort study of breast cancer survivors, were analyzed to investigate the
effect of soy intake after diagnosis on breast cancer prognosis.
147
During
the median follow-up period of approximately 3.9 years, the hazard ratio
associated with the highest quartile of soy protein intake was 0.71 for total
mortality and 0.68 for recurrence compared with the lowest quartile of intake.
In fact, in this study, high soy intake was as protective as tamoxifen use.
In the second study, which was conducted in the U.S. and involved nearly
2,000 breast cancer patients, over the 6-year follow-up period, results
suggested that isoflavone intake may have improved prognosis overall,
and, in particular, among those women taking tamoxifen.
148
However,
among patients who had not previously used tamoxifen, there was an
increased risk associated with higher genistein intake but relatively
few women fell into this category. This raises the possibility that these
findings may have occurred by chance. In a second Chinese study,
Human data suggests that isoflavones do not exert
stimulatory effects on breast tissue, such as tissue
density or cell proliferation in vivo, which are both
markers of breast cancer risk.
Clinical evidence indicates that neither soyfoods nor
isoflavones adversely affect breast tissue.
7
which was conducted in Harbin among postmenopausal women with
estrogen receptor positive and progesterone receptor positive tumors, soy
consumption was associated with an approximate 30 percent decrease
in recurrence although overall mortality was not affected.
149
Interestingly,
although there was no interaction between tamoxifen and soy intake,
which is consistent with the results of the SBCSS, soy intake enhanced
the efficacy of anastrozole, an aromatase inhibitor. These findings are
important in and of themselves, and also because they contradict the
findings in animals.
Finally, the most recently published U.S. study involved 2,736 breast cancer
survivors diagnosed between 1991 and 2000 with early stage breast cancer
who were participants in the Women’s Healthy Eating and Living study.
116
During the median 7.3-year follow-up period, there were 448 new breast
cancer events and 271 deaths. The results showed that as isoflavone intake
increased, risk of death decreased. Women in the highest isoflavone intake
category (cutoff, >16.3 mg/day; median 26.7 mg/day) had a 54 percent
reduction in risk of death (p for trend=0.02). The benefits of isoflavone
intake were most evident in women being treated with tamoxifen.
A recent commentary in the journal Women’s Health concluded that
there is no longer any justification for advising women with breast
cancer to avoid soyfoods.
150
However, the data also does not justify a
recommendation that women should consume soyfoods specifically to
improve prognosis. Rather, the recommendation should be that women
with breast cancer who currently consume soyfoods or wish to consume
them can safely do so. Nevertheless, breast cancer patients should
discuss any dietary changes with their primary healthcare provider.
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Meta-analysis of randomized controlled trials. Clin Nutr. 2008; 27: 57-64.
3. Wu AH, Yu MC, Tseng CC, Pike MC. Epidemiology of soy exposures and breast cancer risk. Br J Cancer. 2008; 98: 9-14.
4. Howes LG, Howes JB, Knight DC. Isoflavone therapy for menopausal flushes: a systematic review and meta-analysis. Maturitas.
2006; 55: 203-11.
5. Gollschewski S, Kitto S, Anderson D, Lyons-Wall P. Women’s perceptions and beliefs about the use of complementary and
alternative medicines during menopause. Complement Ther Med. 2008; 16: 163-8.
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Soyfoods provide high quality protein and are good
sources of well-absorbed protein.
Summary and Conclusions
Soyfoods are unique because they are rich dietary sources of isoflavones,
which are endocrine active substances but different from the hormone
estrogen. Epidemiologic and clinical data suggest that soyfoods can
make important contributions to the health of women, particularly
postmenopausal women. Soyfoods potentially reduce coronary heart
disease through multiple mechanisms and may be especially beneficial
when consumed by young postmenopausal women. Clinical research
indicates that isoflavones alleviate hot flashes although the evidence that
they reduce bone loss is unimpressive. Nevertheless, soyfoods can be part
of a bone-healthy diet as they provide high quality protein and many are
good sources of well-absorbed calcium. Adult soy intake does not appear to
reduce breast cancer risk although evidence suggests that soy consumption
during childhood and adolescence does. As there remains a controversy
over whether soyfoods are contraindicated for breast cancer patients, the
clinical evidence indicates that neither soyfoods nor isoflavones adversely
affect breast tissue. Recent epidemiologic evidence indicates that soy
consumption improves the prognosis of breast cancer patients.
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The 69 farmer-directors of USB oversee the investments of thesoy checkoff to maximize profit opportunities for all U.S. soybean farmers. These volunteers invest
and leverage checkoff funds to increase the value of U.S. soy meal and oil, to ensure U.S. soybean farmers and their customers have the freedom and infrastructure
to operate, and to meet the needs of U.S. soy’s customers. As stipulated in the federal Soybean Promotion, Research and Consumer Information Act, the USDA
Agricultural Marketing Service has oversight responsibilities for USB and thesoy checkoff. For more information, please visit SoyConnection.com.
. above for traditional soyfoods does not
apply to many processed forms of soy.
Soy
WOMEN
Soy connection fact Sheet
by the united Soybean board
2
In most clinical. percent, respectively, of the
total isoflavone content of soybeans.
19
Each gram of soy protein in soybeans and traditional soyfoods is
associated with