Sorting Out the Soy Story
Is it good or bad for you?
I have been trying to sort out the soy story for a very long
time. Last week someone shared a link to a URL for the Weston Price Foundation
that has pages and pages of information about the horrors of soy. One of these
is titled "Teens Before Their Time" and talks about a rise in early
maturity in American girls. They indict soy infant formula and cite a study
done in 1986 called the Puerto Rico Premature Therlarche Study and state that
"the most significant dietary association with premature sexual
development was . . . soy infant formula."(Fallon 2002)
Later when quoting an individual who questioned the Puerto
Rico findings, the Weston Price Foundation article asked "Why would [the
author] leave out any reference to the Puerto Rico study in her review? Is it
because Dupont, owner of Protein Technology Enterprises, is the leading
manufacturer of soy protein isolate?" [The author at that time was
employed at a hospital funded by Dupont.]
As most of you know, I am very committed to getting truthful
balanced information. I was troubled by seeing a group that is priding itself
on providing useful information make comments about the supposed agenda of a
scientific article in this way. So I went and got the citation for the 1985
Puerto Rico study. Now, the original article actually says something very
different from what the Weston Price Foundation implies. Yes, there were a
whole group of girls who showed early sexual maturation. But in those children
who were older than 2 when they sexually matured, there were "no
significant associations" to any of the variables including soy formula.
In those under 2, they found correlations with a maternal history of ovarian
cysts, consumption of various products and soy formula. Even more
astounding to me was the finding that the "statistical associations are
probably not sufficient to explain the reported increase because in over 50% of
the case subjects, there was no exposure to any of the risk factors for which
statistical associations were found."(Freni-Titulaer, Cordero et al. 1986)
So the Weston Price Foundation quoted a finding out of
context and made it sound like something totally different from what the study
actually reported. They basically misrepresented the original data. I use this
example to point to the information and misinformation with which the pro and
con sides of the soy story have lined up. I have now read close to 500
scientific abstracts and articles on the soy story. Here is a very simplified
summary of my own conclusions:
Soy can have both very positive and
The type of soy products used can have
very different effects.
The amount of soy products used has
significantly different effects.
In this discussion, I am going to lead you through a very
simplified analysis of what I have found. It certainly is incomplete, but I
hope it will give you a better understanding of some the issues and ways to
make informed decisions.
The scientific interest in the
role of soy in health was fueled by the observation that women in Asian
countries (Japan, China and Indonesia) had significantly lower levels of breast
cancer than women here.(Setchell 1998)
These findings took a while to sort out and generated some very exciting
dialogue in the scientific literature. (Morton, Arisaka et al. 2002)
Soy isoflavones are estrogenic. This means they are shaped
like estrogen and they go and sit in the estrogen receptors. This can be good
or bad depending on whether you want this effect or how much soy you have.
During menopause, soy can 'soften' the impact of wildly fluctuating estrogen
levels. (Setchell 2001)This is why it is now being marketed as a perfect 'all
natural' solution, a great replacement for hormone replacement therapy.
There are some pretty clear benefits of soy in diet. A few
of these are:
can have an impressive effect in limiting postmenopausal osteoporosis. This is one of the very positive estrogenic
effects. (Scheiber, Liu et al. 2001), (Picherit, Bennetau-Pelissero et
al. 2001), (Arjmandi, Birnbaum et al. 1998)
can improve vaginal health for
post-menopausal women. It helps ward off what is known as vaginal atrophy that
is a thinning of the vaginal wall that comes with aging. (Santen,
Pinkerton et al. 2002), (Baird, Umbach et al. 1995)
contributes to lower cholesterol (this
was shown with soy foods not as supplements). (Anderson, Johnstone et
is heart healthy because it relaxes coronary arteries, reduces inflammation,
reduces blood lipids, homocysteine and blood pressure. (Setchell 2001)
seems to be chemo protective in certain breast cancers. This happens when the soy isoflavones go and sit in
the estrogen sites and block the actual estrogen from signaling for the cancer
cells to grow. This effect is true for those cancers that are made worse by
higher levels of estrogen. (Pagliacci, Smacchia et al. 1994)
contains something called a protease inhibitor that can have powerful anticancer
properties. Protease is an enzyme that is
involved in making new cells. If you stop the process, you keep cancers from
growing. Soy has been shown to have a very powerful effect on some cancers. (Kennedy
seems to have a particularly powerful effect on bladder cancer.(Su, Yeh et al. 2000)
protein intake is a very useful option for those with kidney disease because it is very low stress on the kidneys. (Anderson,
Blake et al. 1998)
Of course, the very
estrogenic effect that creates these desirable benefits can have a down side.
Let's take a look at some of these:
The first of these, and
perhaps that of the most questions comes with the use of soy for infants and
children. That issue is so complex and important that I am going to write a
separate piece about it. Let's take a look at some of the issues for adults.
protein at higher levels can disturb menstrual cycles in younger women (premenopausal) causing delayed
menstruation and mid cycle surges of leutinizing hormones and suppressing FSH.
Both can lead to the body getting confused about when and how to ovulate. (Cassidy,
Bingham et al. 1995)
set of studies showed that adult cheetahs eating a soy diet became infertile and showed changes in their liver enzymes. There has
been debate about whether these findings can be applied to humans but it does
raise some questions that needs more study. (Setchell, Gosselin et al.
Genistein, which is one of the isoflavones in soy, directly blocks the
neurotransmitter GABAA. GABAA quiets the
brain. It calms anxiety and panic. Drugs such as Valium, Librium, Halcyon,
Ambien, Restoril and Klonipin activate GABAA. If you are prone to anxiety/panic
or are taking any of these drugs, taking a soy product will not be a good idea.
This effect does not occur with cooked products such as tofu. (Gumbmann,
Spangler et al. 1986)
Persons taking antidepressants called MAO inhibitors should avoid ALL soy products. (Shulman
and Walker 1999)
of nausea, feet edema and breast tenderness
have been associated with taking genistein, one of the specific soy
isoflavones.(Bloedon, Jeffcoat et al. 2002)
foods (not isoflavones) can inhibit iron absorption. This seems to be a function of the fiber found in
the bean part of soy foods and can be overcome with the use of vitamin C. Wheat
and oat bran have a similar effect. (Cook, Morck et al. 1981)
Soy isoflavones can contribute to thyroid problems by inhibiting one of the steps in a long line of key
actions that make for healthy thyroid function. This particular concern is
often widely cited as the reason not to have soy. But it is important to note
that this effect was only true in iodine deficient diets. Iodine comes from
eating shellfish and iodized salt. (Divi, Chang et al. 1997)
a soy isoflavone, can create heart irregularity such as arthymia. (Paillart, Carlier et al. 1997), (Chiang,
Chen et al. 1996)
inhibitors in uncooked soy used at high levels can create problems in the pancreas. There is some disagreement about the significance
of these, but I would lend caution for people who have impaired pancreatic
function such as diabetics.(Gumbmann, Spangler et al. 1986)
There also seems to be a
connection between soy and something called insulin like growth factor. This is a hormone that mimics insulin in the body.
When our systems work well, a higher level of IGF means we need less insulin.
IGF takes over some of insulin's job. This means we get less of the negative
effects that come with high insulin levels. In one study, the level of IGF was
increased on a "low" isoflavone diet in the study. (About 60 mg. per
day for a 150 lb. person) and showed that higher levels of soy isoflavones
decreased the level of IGF. (Maake,
Yamamoto et al. 1997), (Wangen, Duncan et al. 2000), (Khalil, Lucas
et al. 2002)
Soymilk can reduce hair growth and the dimension of the hair shaft. It can also
effect hair pigmentation. So drinking a lot of soymilk may create skinny, grey
hair. (Seiberg, Liu et al. 2001)
Before the negative concerns spook
you, go back and reread the positive things. As you can see, there are powerful
effects on both sides of the equation. And, you can begin to see why all these
conflicting claims would confuse any of us. After all this reading, my best
sense is that some soy every day is a wonderful aid to health in many, many
areas. This is particularly true if you are a woman who is approaching or in
menopause. But too much soy creates real problems, including a contribution to
weight gain by suppressing IGF and potentially contributing to hypothyroidism
in iodine deficient people.
Many of us were seduced by the claims
that soy is the all-powerful solution to hormone shifts. And we had a lot of
it. Soy powder in shakes, soy lattes, soymilk as an alternative to dairy, soy
cheese, edame at the sushi store, tofu quick and easy. We started getting a
little tubbier; we felt that our metabolism wasn't quite right. We had tests
and nothing showed but we knew something was operating. From what I have read,
overuse of soy can certainly contribute to many of these subtle concerns we
Now, does this mean we chuck it? Absolutely
not. But I think it does mean we start paying attention to what kind and how
much. I do think that using concentrated isoflavones is a not good idea at all.
So what is the right amount? What is too much? Based on all that I have read,
my current thinking is the right amount is one serving
per day. One serving for a woman who is 150-200 pounds
generally will mean between 25-40 mg of isoflavones that come from about
12-20 grams of soy product. Soy products generally have about 2 times the
number of mg of isoflavones per gram of soy. The actual amount you eat should
change according to your weight and age. As you get older and your estrogen
levels diminish, you will want to have more. If you are a smaller person, you
will have less. The idea is not to be scared or compulsive about the numbers,
but simply to learn how much soy you are having. This is exactly the same
process you used in learning to calculate the amount of protein you use. You
get a sense of who you are and then plan your serving size accordingly.
This means if you use a soy protein
powder, you should use a different liquid like oat or almond or cow milk.
[Although I am thinking about the issue that soy fed cows and chickens may
somehow be involved in this story.] (Brown and Setchell 2001)] If you want to
use soymilk as your liquid, then choose a protein powder that does not contain
If you plan on having tofu or tempeh
for another meal, don't have a shake that day. If you are vegetarian, I would
strongly encourage you to rethink the reliance on soy products as your primary
protein source and look to other legume and nut sources as alternatives for
I also strongly advise you not to give your small children soymilk as an
alternative to dairy. I will cover this in my next article on children and soy.
Let me make one final comment about the power of scientific
findings. Many of the studies have what are called confounding variables which
can affect the outcomes in a major way. Yes, the evidence from the breast
cancer rate of Asian women is very compelling, but none of the studies make any
reference to what I believe are 2 key factors in the incidence of breast
cancers - the level of sugars and the proportion of Omega 3 to Omega 6 fatty
acids. I think it is reasonable to assume that the traditional Asian diet is
significantly higher in fish (Omega 3), lower in saturated fat (Omega 6) and
lower in sugars than the typical American diet. So, I am not sure it is just
the soy in the diet. I think the story is bigger than that.
But I hope this discussion has given you some way to make
sense of all the claims. I will continue to have soy as a regular part of my
diet, but plan on having way less than I have been.
Anderson, J. W., J. E. Blake, et al. (1998). "Effects
of soy protein on renal function and proteinuria in patients with type 2
diabetes." Am J Clin Nutr 68(6
Anderson, J. W., B. M. Johnstone, et al. (1995).
"Meta-analysis of the effects of soy protein intake on serum lipids."
N Engl J Med 333(5): 276-82.
Arjmandi, B. H., R. Birnbaum, et al. (1998).
"Bone-sparing effect of soy protein in ovarian hormone-deficient rats is
related to its isoflavone content." Am J Clin Nutr 68(6 Suppl): 1364S-1368S.
Baird, D. D., D. M. Umbach, et al. (1995). "Dietary
intervention study to assess estrogenicity of dietary soy among postmenopausal
women." J Clin Endocrinol Metab 80(5): 1685-90.
Bloedon, L. T., A. R. Jeffcoat, et al. (2002). "Safety
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Brown, N. M. and K. D. Setchell (2001). "Animal models
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Cassidy, A., S. Bingham, et al. (1995). "Biological
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Chiang, C. E., S. A. Chen, et al. (1996). "Genistein
directly inhibits L-type calcium currents but potentiates cAMP-dependent
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Cook, J. D., T. A. Morck, et al. (1981). "The
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Divi, R. L., H. C. Chang, et al. (1997). "Anti-thyroid
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inclusion of whole soy foods results in significant reductions in clinical risk
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(c)Kathleen DesMaisons 2006. All rights reserved.