Being Vegan and Eating Soy: Myths, Truths, and Everything in Between

[Guest guest]

Being Vegan and Eating Soy: Myths, Truths, and Everything in Between

by Christa Novelli, M.P.H.

*friendly forward* Spiritually_Speaking

 

Soy foods have received a great deal of attention in the media in recent years.

Very little that the public hears about soy is neutral. Depending upon whom you

choose to believe, soy is either a wonder food or the next asbestos. Even among

professionals in the field of nutrition and other sciences, there is much

confusion about the conflicting information drawn from the countless research

articles published each year on soybeans and their derivatives. While it is

unlikely that I will address all concerns or cover every study ever conducted on

the health effects of soy consumption, I hope to give a clearer picture of what

the research regarding soy and human health tells us.

 

First, we need to have a basic understanding of what is included in the term

" soy foods. " Soy foods encompass a wide variety of items including edamame

(whole soybeans), soy flour, soymilk, tofu, soy protein isolates, texturized

vegetable protein (TVP), soy oil, and fermented soy products such as tempeh and

miso. Adding to this list are all of those processed items that are made from

these soy products including soy " meats, " soy cheeses, soy " ice creams, " among

many other items. One may be surprised to find out how many foods contain some

form of soy (soy flour and soy lethicin are often found in cereals, cake mixes,

granola bars, and a whole host of other items). Obviously, vegetarians and

vegans are not the only Westerners who eat soy products as a regular part of

their diet.

 

As is often the case when a food or medicine is presented as the new " wonder

drug, " soy has experienced a backlash in recent years. A few organizations, most

notably the Weston A. Price Foundation (WAPF) and the innocuous sounding Soy

Online Service (SOS) in New Zealand, have seized upon any negative studies

involving soy products (usually the primary isoflavone found in soy, genestein)

and are seeking to have soy foods and formula removed from the public

marketplace on the grounds that they cause a myriad of problems ranging from

cancers to brain atrophy to immune and endocrine system disorders. As one

researcher very accurately noted in his response to an editorial appearing in

the professional journal, Leukemia, which has been oft cited as " proof " of soy's

deleterious effects, medical journals are no longer a safe forum for scientists

and doctors to discuss and debate new hypotheses with one another. These

publications, and in particular the abstracts published in these journals, are

increasing being accessed by the public especially in the age of the Internet.

 

For those of you unfamiliar with scientific writing, an " abstract " is a brief

summary of a study's research question, methods and conclusion(s). Abstracts for

many scientific articles can be accessed by the public, free of charge, online

at the National Library of Medicine's website, PubMed and also on Med Line.

While I used to be a proponent of " doing your own research, " by searching for

information on these websites, the more I have seen about how these abstracts

are being used and interpreted the less inclined I am to advise the lay public

to draw conclusions from abstracts that can be found on the internet. It is very

questionable science to start with your conclusion in mind and then search for

any and all studies to support said conclusion. Unfortunately, that is exactly

what many of the soy detractors appear to have done, aided by abstracts found

online.

 

A good analogy-- if I started with the conclusion that eating oranges and

broccoli was going to cause cancer, I could actually find a number of articles

that showed that a component of these foods (vitamin C) has been shown in some

trials done on animals and cell cultures to proliferate tumors. I could then

publish articles warning of the dangers of oranges and broccoli and cite these

studies as " proof. " Of course, I would be going against the much greater body of

evidence that shows the exact opposite effect.

 

Another problem that I have found in looking at the research cited by the

detractors of soy is that one can come to a conclusion that is at complete odds

with the research you are citing by reading just the abstract of an article. For

instance, the WAPF has a link on their website that purports to show the dangers

of soy by citing a large number of research studies with direct quotes drawn

from the abstracts of these published articles. One example includes a study of

soy formula published in the American Journal of Clinical Nutrition in 1998 [1].

On the WAPF site, pieces of the abstract are quoted stating that the researchers

found significantly elevated plasma isoflavone levels (plant estrogens found in

the blood stream) of infants fed soy-based formula and that this may exert

long-term health effects for these infants. What one would find, if he bothered

to read the entire article, was that the researchers found health benefits (i.e.

- " effects " ) for children with increased levels of isoflavones in their blood

stream - the exact opposite of what WAPF is attempting to assert.

 

Similarly, this same site, as well as a number of others such as theomnivore.com

and bullz-eye.com, mentions numerous articles that found that soy consumption by

males reduces serum (blood) testosterone levels [2] [3] [4]. These studies are

cited in online articles with titles like: Soy lives up to its reputation as the

breakfast of weenies. WAPF quotes one of the abstracts [3] as testifying that

" replacement of meat protein with soyabean protein, as tofu, may have a minor

effect on biologically-active sex hormones which could influence prostate cancer

risk. " [Emphasis mine] What the term " influence " in the study findings actually

meant was reduce, not increase risk. In addressing a similar study [4], WAPF

casts doubt on the authors of the study when it questions why they focused on

their findings that consuming soy reduced the risk of prostate disease and

arteriosclerosis, but failed to note that " testosterone levels fell in the

volunteers eating soy but researchers did not stress this alarming finding in

their conclusion. " There was no reason for the authors to consider a reduction

in testosterone an " alarming finding. " In fact, the reduction in testosterone

levels was likely the reason for the reduction in disease risk much the same as

reduced estrogen in the blood stream of women reduces breast cancer risk.

 

So, what does the research show? I will attempt to answer that question by

addressing the various health problems that soy has been alleged to prevent and,

conversely, cause or exacerbate. Some of the major diseases and health problems

that soy has been associated with (in a positive or negative manner) include

breast cancer, other cancers, neurodegenerative diseases and dementia ( " brain

atrophy " ), thyroid disorders, infertility, and disorders or problems specific to

males (often referred to as " demasculinization " ). Then there is the whole

separate issue of soy formula, which I will address on its own.

 

Cancer

Allegation:

The argument has been put forth that the phytoestrogens (plant estrogens)

contained in soy promote the growth of cancers.

 

Reality:

While a few studies have found that animals who are implanted with cancer cells

and then fed soy protein isolates show increased growth of the cancer cells, the

majority of the research shows soy to have an inhibitory effect on cancer

growth. A recent meta-analysis of the literature relating to soy and cancers of

the breast, colon, and prostate, found that individuals who consumed soy had a

reduced risk of developing all three of these types of cancers [5].

 

When results are not in favor of their conclusion, the opponents of soy often

call into question the research method used. Meta-analyses have been questioned

as a less than valid research method. SOS has stated in their Marketplace

Newsletter that meta-analyses are, " a method upon which many in the scientific

community frown. "

 

This same newsletter also claims that meta-analyses that show benefits to

consuming soy are flawed because, " there is also the added temptation for

researchers, particularly those funded by industry, to omit studies that prevent

desired conclusions. " Omission of studies that find the opposite of what one has

already concluded is certainly a significant flaw and the conclusions drawn by

meta-analyses are appreciably dependent upon proper use of the research tool. A

meta-analysis involves conducting a systematic review of the research on a

particular topic. If one uses a narrative approach rather than a systematic

approach, that is picks and chooses which studies to include based upon personal

bias, there is plenty of room for inaccurate conclusions. The key words here

being systematic (an organized, unbiased synthesis of the data) versus narrative

(an account based upon personal selection).

 

In fact, properly conducted meta-analyses are one of the more powerful

statistical tools for assessing the effect of health interventions and are not

" frowned upon " by any scientific community with which I am familiar. The

meta-analysis, to which I referred, above, was systematically conducted and

showed no apparent bias.

 

With that aside in mind, women may want to exercise some caution if they have a

history of estrogen dependent breast-cancer. While there is no definite proof

that consumption of phytoestrogens increases the risk of a reoccurrence, and

some studies even show a reduction in risk of reoccurrence, the jury is still

out in this area. There is some indication that consumption of soy isoflavones

may interact with the anti-breast cancer drug, tamoxifen, reducing its efficacy

[6]. While this effect is not certain, it would be wise to discuss your

consumption of soy products with your doctor if you have a history of breast

cancer.

 

The most logical course to take if one is concerned about the possible negative

effects of plant estrogens contained in soy is to avoid consuming highly

processed forms of soy, or reduce consumption of those products. It has been

suggested by a few scientists that the degree of processing effects how soy

phytoestrogens will react with the human body, with the more highly processed

soy products (especially soy protein isolates) exerting a more estrogenic effect

in the body. Just to put this in perspective, some of the same researchers who

have found estrogenic effects on animals when feeding them high concentrations

of soy protein isolates, have also found similar estrogenic effects for isolates

of other plants - namely cabbage and brussel sprouts [7]. No one is suggesting

that we all stop eating cabbage because it obviously offers significantly more

benefits than it does risks. We just generally do not eat extracts of

freeze-dried cruciferous vegetables. The same should hold true for soy and any

other food - the closer to its whole form as possible is probably the best

choice.

 

Brain Health

Allegation:

Soy causes Alzheimer's disease, dementia, and reduced brain functioning.

 

Reality:

The great majority of the research relating to soy consumption and brain health

shows soy to have a protective effect on the brain, not a damaging effect on the

brain. One article that has frequently been cited as " proof " that soy damages

the brain found some possible benefits and some possible harm for male rats fed

a diet high in phytoestrogens [8]. The researchers who conducted this study have

also conducted a number of other studies wherein the conclusions were that soy

phytoestrogens are protective to the brain.

 

Edwin Lephart, the lead researcher on the above noted study, has this to say in

response to his article being cited as proof of soy causing neurodegeneration of

the brain: " In general, phytoestrogens, and more specifically isoflavones,

appear to be neuroprotective. Meaning these molecules protect the brain cells

and brain function. The research that you state via the Price foundation citing

our article is but one study. There are many studies and many molecules that

isoflavones influence in the brain and when one examines the overall effect of

isoflavones the current evaluation, in my opinion, is that phytoestrogens

derived from soy are neuroprotective. [9] "

 

Thyroid Health

Allegation:

Soy consumption reduces thyroid function and/or causes thyroid cancer.

 

Reality:

Some older studies of infants fed soy-based formula not fortified with iodine

showed reduced thyroid functioning in those infants. Further research has shown

that, in the absence of an iodine deficiency, soy does not reduce thyroid

function [10]. In relation to infants with congenital hypothyroidism, there is

not yet complete consensus amongst the scientific community as to whether soy

formula complicates this pre-existing condition. If you have an infant with

congenital hypothyroidism, again, soliciting the advice of your doctor or health

care provider would be a wise decision.

 

As far as thyroid cancer is concerned, large population-based studies show that

soy not only does not increase the risk of thyroid cancer, it exerts a

protective effect [11].

 

Infertility and reproductive health

Allegation:

Soy causes infertility, hormonal imbalances, hypospadias, and desmasculinization

of males.

 

Reality:

A few studies of the offspring of rodents who were fed soy isolates during

pregnancy and lactation and rodents who were injected with soy isoflavones in

infancy have found evidence of negative reproductive outcomes. However, there is

a significant difference in the amount of estrogen to which fetal rats and fetal

humans are normally exposed. Fetal rats are normally exposed to very small

quantities of estrogen in utero whereas human fetuses are normally exposed to

large quantities of estrogen in utero - this is without any soy consumption on

the mother's part. It has been suggested that rats, unlike humans, are not meant

to be exposed to significant quantities of estrogen in utero and their

reproductive organs are, therefore, more biologically sensitive to the effects

of isoflavones. [12]

 

Whatever the mechanism for the poor outcomes for the rodents, these results have

not been replicated in humans. In fact, research on human infants exposed to soy

in utero and during infancy has found no statistically significant differences

in sexual development or reproductive health other than one study that found

slightly longer menstrual periods in women who were fed soy formula as infants

[12]. Clinical studies of infants fed soy formula, arguably the infants with the

highest exposure to soy, have found no hormonal defects, no increase in

infertility and normal sexual maturation. [13] [14] [15] [16]

 

The one human study that implicated a vegetarian diet during pregnancy as a

cause of hypospadias [17] (a congenital defect of the male genitalia in which

the opening is not at the tip of the penis) should not be entirely dismissed,

but is certainly not conclusive either. The researchers followed a large cohort

of pregnant women in Britain and looked at many factors that could influence the

development of hypospadias, including maternal diet. They then followed up to

determine which factors were associated with a greater instance of hypospadias.

Among those factors considered, the only ones that increased the risk of having

a male child born with this defect were iron supplementation during pregnancy,

being vegetarian during the pregnancy, and/or influenza during the first

trimester.

 

Without looking any further, these findings may be alarming. However, we need to

consider what aspect of their environment may have increased the instance of

hypospadias among the boys born to the vegetarian mothers - soy is certainly not

the only possibility and perhaps not even the most logical suspect once the

remainder of the findings are considered. The researchers do hypothesize in the

abstract of their article that " vegetarians have greater exposure to

phytoestrogens than do omnivores, these results support the possibility that

phytoestrogens have a deleterious effect on the developing male reproductive

system. [18] "

 

We must understand that a hypothesis is only a tentative explanation and not a

tested theory. Yes, it is possible that phytoestrogens played a role, but it is

also possible that the pesticides on the larger quantities of produce eaten by

the vegetarian women played a role, another hypothesis that the researchers

offer in this paper. (Very few of the women in the study ate organic produce. Of

those who did, none had a son born with hypospadias, but the numbers of women

who fell into this category - consuming only organic produce - was so small that

it was not possible to calculate if the protective effect of organic produce was

statistically significant.)

 

Again, if we bothered to read the entire article, we would find the statement

that, " the association of hypospadias with a vegetarian diet was not obviously

explicable by the components of a vegetarian diet. There were differences in the

proportion of hypospadias cases born to mothers consuming soya milk or other

products, but they were not significant, possibly because there were too few

mothers who reported consuming such foods. [19] " [Emphasis mine] Thus, there was

an association with being vegetarian during pregnancy and increased risk in

having a son born with hypospadias, but there was not an increase in risk

related to consuming the two soy products that the dietary questionnaire

accounted for: soy milk and soy " meats. "

 

Without a more thorough analysis of the dietary habits of pregnant women, it is

impossible to determine if soy was the cause of the increased incidence of

hypospadias among the vegetarian women included in this study or if there was

some other dietary or other environmental cause. Further research is warranted,

but until these findings are replicated with a more careful dietary analysis, we

really do not know what caused the increase in hypospadias in the infants in the

study.

 

Soy Formula

Then we have the issue of soy formula. The feeding of soy-based formula to

infants is highly contentious. All doctors, scientists and health professionals

with whom I spoke (myself included) would recommend breast feeding over any kind

of formula when at all possible. With that aside, it is hard to determine the

true effects of soy formula on human infants because so few studies have been

done on human infants. The Arkansas Children's Nutrition Center based at the

University of Arkansas for Medical Sciences (UAMS) has a research team who is in

the process of conducting the largest and most complete study to date of infants

fed soy formula, cow's milk formula and human breast milk. The lead researcher

for this study, Tom Badger, was kind enough to answer some questions for me via

email and to speak with me on the phone.

 

Dr. Badger stated that the number of children fed soy formula in the U.S. is

larger than in any other nation (25% of the four million infants born in the

U.S. each year are fed soy-based formula). This sets the U.S. up as the perfect

location for testing the long-term effects of this feeding choice. Dr. Badger

estimates that 1 million infants are fed soy formula each year in the U.S. and

" thus, we have a lot of experience with this food source for infants. These

children grow and develop normally and have disease and disorder rates equal to

those of infants fed milk-based formula. All of our research thus far suggests

that there are health benefits rather than adverse effects of consuming soy

formula. Therefore, any adverse effects would need to be very subtle or occur

much later in life, say after age 40-45 years. [20] "

 

The Arkansas study currently has hundreds of children enrolled with more

children being enrolled every week. The oldest children in the study are three

years old at this point and have been followed since four weeks of age. The

children in the study are seen every month for the first year of life with each

visit lasting between two to six hours. The study participants are seen yearly

thereafter until age six, with the hopes that funding will be extended to allow

the children to be followed through puberty. Thus far, all evidence from this

study (which includes body composition, brain growth and function,

endocrinology, and metabolism) shows no difference in the children fed soy-based

formula versus cow's milk-based formula.

 

Dr. Badger's team did an in-depth review of prior studies that showed adverse

effects on young animals who were injected with or fed soy derivatives. They

spoke with the researchers of those studies and concluded that there were major

flaws in the studies and/or there were other factors that made the studies

inapplicable to human infants. Dr. Badger did note that animal studies are not

always flawed by virtue of the fact that they were done on non-human animals and

the flaws found varied depending on the studies.

 

Animal Studies

In general, the concern with the animals studies that relate to isoflavones fall

into a few areas. One concern is that many of the studies that found increases

in cancer dealt with immunocompromised animals and/or female animals whose

ovaries and uteruses had been removed. An average adult or child has not had a

complete ovo-hysterectomy nor is s/he immunocompromised. It is not possible to

generalize to a whole population based upon a small component of that population

with different circumstances.

 

Also, some animal models inject purified isoflavones into rats. Isoflavones

found in soy are bound into a completely different form in the whole food (soy

milk and tofu are included in this discussion as " whole foods " as the processing

involved - heat from cooking and blending of the whole soybeans with water and

coagulants - does not turn them into purified isoflavones). Soy consumed as a

whole food, including soy milk, tofu and fermented soy products, must be

metabolized in order to extract the isoflavones. Feeding or injecting an animal

with purified isoflavones skips over this metabolic process and is basically the

same as giving the animal high doses of a drug.

 

Unfortunately, animal studies that include feeding soy products (not just

purified isoflavones) cannot always be easily translated into human effects

either. For instance, studies that have found reduced testosterone levels in

male monkeys fed soy formula, failed to take into account the different

intestinal bacteria found in monkeys that are not found in humans. Despite our

close genetic relation, monkeys have bacteria in their intestines that

metabolizes daidzein (a soy isoflavone) into a highly estrogenic substance;

humans do not have this same bacteria.

 

The animal models can be a good place to start, but should not be relied upon

for making health decisions for humans without replication in human subjects. At

this point, those studies that have been conducted on humans, and even the

majority of those conducted on animals, have leaned towards the conclusion that

soy is beneficial to health, not detrimental.

 

What forms of soy and how much soy should you be eating?

Since most of the studies that raise concerns about soy consumption seem to

focus on pre-metabolized isolates or other similarly processed forms of soy, the

wisest choice to is to choose to eat soy foods as part of a balanced diet and in

the least processed form available. Soy can be a valuable source of protein in a

vegetarian or vegan diet, but it should not be relied upon as the sole source of

protein. We should also be careful with drawing the conclusion that, if a little

bit of something is good, a lot must be even better. Variety in your diet is an

excellent way to ensure balance and good health.

 

Choosing traditional and less processed forms of soy (such as tofu, miso,

tempeh, edamame and even soy milk) over highly processed soy foods (such as soy

cheeses, soy meats, and soy protein isolates) is likely to be a safer choice, as

well. We all need our treats sometimes and the research does not support the

conclusion that eating a little vegan soy cheese on your pizza is going to cause

health problems, so go ahead and allow yourself some indulgences every now and

then if you want to. Just don't make soy cheese and soy sausage casserole the

mainstay of your diet.

 

Further Information

While it can be difficult to find an unbiased source of information on soy,

there are some good websites where you can get further information, some more

impartial than others. I would recommend reading some of the following articles

and checking out some of the following websites:

 

Information on interpreting studies on soy

 

Dr. McDougall's view on soy

 

John Robbins' view on soy

 

The US Department of Health and Human Services' Agency for Healthcare Research

and Quality (AHRQ)'s assessment of the research on human consumption of soy

 

There are also some websites that I would avoid if you are not looking for scare

tactics.

These include:

 

The Weston A. Price Foundation's website

 

The Soy Online Service's website

 

Nutritional supplement manufacturer, Roex's website

 

Mt. Banahaw Health Product Corporation's website (strong ties to WAPF)

 

Dr. Mercola's view on soy

 

Footnotes:

1. Setchell KD, et al. Isoflavone content of infant formulas and the metabolic

fate of these early phytoestrogens in early life. Am J Clin Nutr 1998 Dec;68(6

Suppl): 1431S-1435S.

2. Nagate C, et al. Inverse association of replacing meat with soyabean in the

diet on sex hormone concentrations in Japanese men. Nutr Cancer 2000; 36(1):

14-8.

3. Habito RC, et al. Effects of replacing meat with soyabean in the diet on sex

hormone concentrations in healthy adult males. Br J Nutr 2000 Oct;84(4): 557-63.

4. Gradern-Thorpe D, et al. Dietary supplements of soya flour lower serum

testosterone concentrations and improve markers of oxidative stress in men. Eur

J Clin Nutr 2003 Jan;57(1): 100-6.

5. Badger TM, et al. Soy Protein Isolate and Protection Against Cancer. J Am Col

Nutr 2005: 245(2): 146S-9S

6. Ju YH, et al. Dietary genistein negates the inhibitory effect of tamoxifen on

growth of estrogen-dependent breast cancer (MCF-7) cells implanted in athymic

mice. Cancer Res 2002 May; 62(9): 3474-7.

7. Ju YH, et al. Estrogenic Effect of Extracts from Cabbage, Fermented Cabbage,

and Acidified Brussel Sprouts on Growth and Gene Expression of

Estrogen-Dependent Human Breast Cancer (MCF-7) Cells. J Agric Food Chem 2000;

48(10): 4628-34.

8. Lephart, et al. Phytoestrogens decrease brain calcium-binding proteins but do

not alter hypothalamic androgen metabolizing enzymes in adult male rats. Brain

Res 2000 Mar 17; 859(1): 123-31.

9. Personal communication, August 2005

10. Bruce B, et al. Isoflavone supplements do not affect thyroid function in

iodine-replete postmenopausal women. J Med Food 2003 Winter; 6(4): 309-16.

11. Haselkorn T, et al. Why Are Thyroid Cancer Rates So High in Southeast Asian

Women Living in the United States? The Bay Area Thyroid Cancer Study. Cancer

Epidemiology Biomarkers and Prev 2003 Feb; 12: 144-50.

12. Merritt RJ and Jenks BH. Safety of Soy-based Infant Formulas Containing

Isoflavones: The Clinical Evidence. J Nutr 2004 May; 134: 1220S-4S.

13. Munro IC, et al. Soy Isoflavones: a safety review. Nutr Rev 2003; 61:1-33.

14. Strom BL, et al. Exposure to soy-based formula in infancy and

endocrinological and reproductive outcomes in young adulthood. J Am Med Assn

2001; 286:807-14

15. Churella HR, et al. Growth and protein status of term infants fed soy

protein formulas differing in protein content. J Am Coll Nutr 1994; 13:262-7.

16. Businco L, et al. No oetrogens hormonal effects in long-term soy formula fed

children. J Allergy Clin Immunol 1999; 103:S169.

17. North K and Golding J. A maternal vegetarian diet in pregnancy is associated

with hypospadias. The ALSPAC Study Team. Avon Longitudinal Study of Pregnancy

and Childhood. British J Urology 2000 Jan; 85(1): 107-13.

18. Ibid. Pg. 107

19. Ibid. Pg. 111

20. Personal communication, August 2005

 

Christa has a Masters degree in Public Health and works part-time as a health

educator. She lives in Colorado with her husband and two daughters. Christa has

been vegetarian for 20 years and vegan for nearly 17 years.