Is It Safe to Eat Soy? ~~ Edith

[Guest guest]

[Chat-CVC] Is It Safe to Eat Soy? ~~ Edith

 

 

A number of times the question of the varied opinions on the value of Soy in our

diet has come up. I just read a very good report on this topic. So, I thought

that I should post the following article from the list:

DietaryTipsForHBP that was provided by Joanne Guest. The

source for the article is at the end, with the link in case you would like to

check this out further. Love, Edith

 

 

 

~*~*~*~*~*

 

Soy: Pros and Cons Is It Safe to Eat Soy? By Virginia Messina, MPH, RD &

Mark Messina, PhD

 

 

No doubt you've heard lots of good things about soyfoods. According to a health

claim sanctioned by the FDA, they can help to fight heart disease. 1 They may

also make your bones stronger. 2, 3 And the biggest news about soyfoods over the

past decade has been that they contain cancer-fighting compounds.

 

 

Making your way through the controversy can be confusing. Hopefully, we can

tread a more even path here and convince you that, while soyfoods may not be the

answer to all your problems, and while there certainly are a few unanswered

questions, you can include soyfoods in a balanced and healthful vegan diet.

 

 

In making our way through this quagmire, it is important to recognize some

important facts about scientific research. It is a rare situation where every

single study on a subject is in agreement. There are always a few that sit in

direct contrast to the majority of the studies. So it is never a good idea to

suggest broad conclusions or recommendations based on one or two studies. By

picking and choosing individual studies carefully enough, you can prove just

about anything you would like about nutrition. That's why health experts look

at all the research and pay attention to the totality of the evidence, not just

to a few studies. Many of the studies that have concluded that soy is

unhealthful have used animals as subjects. Drawing conclusions about human

health from animal research can be very misleading. For example, broccoli and

other cruciferous vegetables contain a compound (called indole-3 carbinol) that

is an anticarcinogen in humans. But in some other species, it causes cancer. 5

If we looked only at the results of the studies in those species, the FDA would

no doubt ban broccoli and cabbage from grocery stores.

Even so, soyfoods are significant in the diets of many vegans and it is worth

taking a look at some of the claims against them.

 

 

Soyfoods and Thyroid Many foods contain goitrogens, compounds that interfere

with thyroid function (and in extreme cases can cause an enlarged thyroid,

called a goiter). Along with soyfoods, millet, cruciferous vegetables and other

foods contain goitrogens. Generally, these foods cause problems only in areas

where iodine intake is low since this mineral is important for thyroid function.

The effects of iodine deficiency can be made worse if the diet is high in

goitrogens.

 

 

Although a concern about soy and thyroid function may be news to many vegans, it

has actually been a focus of research for more than 70 years. 6 Between 1951

and 1961, this research took on a special importance when about 10 cases of

goiter were diagnosed in infants who had been fed infant formula made from soy

flour. These old studies form some of the basis for arguments that soy is

dangerous for infants. However, the situation for today's soy formula-fed infant

is very different. Since the 1960's,soy-based infant formula has been made from

soy protein isolate (which does not contain the goitrogen component; soy flour

formulas did) and it is fortified with iodine. No cases of goiter have been

diagnosed in infants fed this formula in the past 40 years. Nor is there any

evidence that consuming soy causes thyroid problems in healthy, well-nourished

people who have adequate iodine in their diet. . 7-10 However, it is possible

that eating a diet with generous amounts of soyfoods could be a problem for

people whose iodine intake is marginal. And that might just include some vegans,

since the main sources of iodine in western diets are fish and milk. But the

appropriate response to this is not to limit healthful soyfoods; it's to get

enough iodine. Vegetables have varying amounts of iodine depending on where they

are grown. In some parts of the world--specifically northern Europe--vegans may

have low intakes of iodine.

 

 

Foods that can supply iodine to vegan diets are sea vegetables, although

contents vary quite a bit. Fortified foods are also a good source. Iodized sea

salt and kelp are about the most reliable sources. Vegans should be sure that,

when they season foods with salt, it is iodized. If this isn't a regular part of

your diet, use an iodine

 

 

supplement. Conclusion: Soyfoods may contain goitrogenic compounds as do

other foods. There is no evidence that eating soyfoods regularly causes thyroid

problems in people who eat a balanced diet. Vegans should make an effort to

include adequate sources of iodine in their diet.

 

 

Soyfoods and Cognitive Function A study conducted in Hawaii called the

Honolulu Heart Study came up with a surprising finding. The study looked at

Japanese men residing in Hawaii and aimed to compare diet to risk of dementia.

The researchers found that those men who ate tofu most frequently during their

mid-40's to mid-60's showed the most signs of mental deterioration in their 70's

to early 90's. 11 In this study of over 3000 men, intake of 26 foods, including

tofu, was recorded between 1965 and 1967 and again in 1971 to 1974. Cognitive

test performance was assessed between 1991 and 1993 and the researchers also

looked at brain shrinkage through autopsy data of the men who died during the

study. Tofu consumption of just two to four servings per week was associated

with poorer test performance and more brain loss. Not only that, but the wives

of men who ate tofu also showed more signs of dementia. The study raised lots

of questions.

 

 

For one thing, how could this be when it is known that dementia rates are lower

in Asian countries than in western countries and when Japanese lifestyle has

actually been associated with better cognition in old age? Many have used this

as an argument to show that the Hawaii study results must be wrong. But

comparing rates of dementia across cultures doesn't really tell us much in this

regard because there are too many differences between the lifestyle in Japan and

the lifestyle in Europe and North America. And criteria for diagnosing dementia

vary across cultures. To get the real story, we would need to compare frequent

tofu consumers in Japan to people in Japan who don't eat tofu. And that study

hasn't been done yet. Furthermore, there is a possible biological explanation

for the findings. Soybeans contain isoflavones, which are weak estrogens. They

fall into the category of estrogen-like compounds known as SERMS--selective

estrogen receptor modulators. 12 This means that they have estrogenic effects

in some tissues and anti-estrogenic effects in others. Estrogen may have a

positive effect on brain tissue but the researchers of the Hawaii study

suggested that isoflavones may have antiestrogenic effects on the brain. Of

course, we can't know this from the Hawaii study. This was an epidemiological

study, so it doesn't show cause and effect. It merely shows that two things

occur together. Since the researchers measured intake of only 27 foods and were

not able to control for every single lifestyle factor, it is possible that tofu

consumption is a marker for some other factor that affects cognitive function.

This would make tofu an innocent bystander. Results of other studies suggest

this is true. Results of three clinical studies, only one of which has thus

far been published in full manuscript form, suggest soy and isoflavones have

beneficial effects on cognition. In the published study, young adult men and

women who consumed a high soy diet for 10 weeks experienced significant

improvements in short-term and long-term memory and in mental flexibility. 13

The other two studies which have been presented at scientific meetings, found

that isoflavone supplements, when taken by postmenopausal women, improve

cognitive function. Even with these findings, we really have very little

information on how soyfoods consumption might affect cognitive function. It's

important to note though that studies of Seventh-day Adventists, many of whom

have consumed soyfoods all of their lives, suggest that this group experiences

less dementia in old age than the general population. 14 This may reflect an

overall healthier lifestyle or higher education (which is linked to better

cognitive function in old age). We simply don't know. We do know that there

are ways to protect cognitive function as we age. Eating a diet high in

antioxidants (which means a plant-based diet), engaging in regular exercise, and

stimulating the brain through learning and problem-solving activities, all seem

to be associated with better cognitive aging. 15-19

Conclusion. One study has suggested a link between tofu consumption and poorer

cognitive function in old age, but this is an epidemiological study. Therefore

it doesn't show cause and effect. It did not look at diet extensively enough to

draw firm conclusions. And there are no other studies to support it and three

clinical studies suggest soy and isoflavones have beneficial effects on

cognition. At this point, there is no reason to believe that eating soyfoods is

harmful to brain aging.

 

 

Soyfoods and Mineral Absorption Critics of soyfoods say that soy is high in

phytates which inhibit absorption of iron, zinc, and calcium.

 

 

But the absorption of calcium from soyfoods is actually surprisingly good given

the phytate content of those foods. 20, 21 Not only that, but a number of

studies have shown that the isoflavones in soyfoods protect bone health. 2 and

that soy protein when substituted for animal protein decreases urinary calcium

excretion.

 

 

3 So getting calcium from soyfoods that are either naturally rich in this

nutrient or are fortified with it, seems like a very good idea. However, there

is certainly some research showing that vegan women have low calcium intakes.

Contrary to popular opinion, there is little evidence that vegans have better

bone health than people eating other types of diets and there is some evidence

that links their lower calcium intake with poorer bone health. While this is a

potential problem, it has nothing to do with any shortcomings of soyfoods. And

it is an easily resolved problem. Vegans simply need to make sure they meet

recommendations for calcium (1,000 mg a day for adults age 19-50) either through

natural food sources of this nutrient, fortified foods or supplements. It is

also important to make sure that your diet is well-balanced with adequate

protein and with adequate vitamin D. While too much protein may be detrimental

to bones, so is too little. And, while it is possible to make adequate vitamin D

through sun exposure, it isn't a sure thing in many parts of the world so

supplements or fortified foods are a good idea.

 

 

But it is true that, all other things being equal, phytates inhibit the

absorption of iron and zinc. Soybeans are rich in phytate and vegan diets are

especially high in phytate. It is very well documented that vegetarians absorb

iron less well than meat eaters and have lower stores of iron in their bodies.

But the implications of this aren't clear. Vegetarians don't appear to be any

more likely to actually develop iron deficiency. 22 And, because high levels of

iron may raise risk for heart disease, it may be that having lower but adequate

stores as vegetarians do is the ideal situation. 23 Soy protein also inhibits

absorption of iron, making soyfoods a poor source of available iron even though

they contain this nutrient. So the critics are correct that people should not

depend very much on soyfoods to meet their iron needs. And it may also be that

the protein in soy inhibits absorption of iron from other foods. But this is not

a reason to avoid soy. Rather, vegans should make sure that their diets are

rich in good sources of iron--grains, beans, dried fruits, nuts, seeds, and many

vegetables--and they should also make sure they get adequate vitamin C at meals.

Vitamin C boosts absorption of iron from many plant foods. However, it is not

enough to have a diet high in vitamin C. If you take a vitamin C supplement in

the morning or consume a couple glasses of orange juice between meals, this

won't affect your iron absorption. The vitamin C must be consumed at the same

time as the iron.

 

 

Zinc is also poorly absorbed from soyfoods. Vegans generally have a lower intake

of zinc and lower absorption than meat eaters and probably than lacto-ovo

vegetarians. It's a nutrient that deserves some attention in vegan diets. But

again, avoiding soyfoods is not the way to ensure adequate amounts of

bioavailable zinc. Rather, making sure that your diet is rich in zinc-rich

foods--nuts, seeds, whole grains, and legumes--is important.

 

 

Conclusion: Soyfoods can be good sources of well-absorbed calcium whether they

are natural sources of this mineral or are fortified with it. They may also

provide other factors that help to improve bone health.

 

 

Vegans should make sure their diets are adequate in calcium and vitamin D and

are generally well-balanced with adequate protein. Iron deficiency does not

appear to be a problem for vegans--at least no more so than for people eating

other kinds of diets. But, given that it is a common world-wide deficiency,

everyone should make sure they eat plenty of iron-rich foods and vegans should

consume good sources of vitamin C at meals. Likewise, it is important to eat

plenty of zinc-rich foods every day.

 

 

Soy and Breast Cancer

 

 

All of the popular discussion surrounding soy actually started out because of

evidence suggesting that soy, likely because of the isoflavones, reduced breast

cancer risk by inhibiting the effects of estrogen. 24 Some of the evidence for

this comes from the observation that breast cancer rates are lower in Asian

countries than among western women. However, many factors that differ among

cultures might affect breast cancer risk. And it is interesting to note that,

within Asian cultures, there is little epidemiological evidence that shows soy

consumption is protective against breast cancer. A few short term clinical

studies have suggested that soy consumption has estrogenic effects in the breast

tissue of young--that is, premenopausal--women. 25, 26 This would suggest a

possible increased risk for cancer. The significance of these short term studies

isn't clear however. For example, the drug tamoxifen, used to treat breast

cancer, actually has estrogenic effects when used for the short term, but

antiestrogenic effects over the long term. There are also a number of other

considerations. First, research in laboratories on breast cancer cells has shown

that small doses of the soy isoflavone genistein cause cells to replicate

whereas large doses inhibit cell growth. Furthermore, there is some evidence

that eating soy early in life--especially during puberty--helps to protect girls

from breast cancer later in life. 27, 28 This would help explain why Asian

women--most of whom grow up on soyfoods--have lower rates of breast of cancer

than even western vegetarians, who might not begin eating soy until adulthood.

Finally, soy isoflavones have a number of effects that are possibly protective

against cancer and that have nothing to do with their estrogenic or

antiestrogenic effects.

 

 

For example, genistein may inhibit the growth of the blood vessels that support

tumor growth and may also inhibit enzymes that promote cell growth. Soy may

alter estrogen metabolism in a way that protects against cancer. Also,

year-long studies have found that soy or isoflavones either have no harmful

effect or favorably affect breast tissue density, which is an indicator of

breast cancer risk. 29 For women who have already had breast cancer and whose

cancer is estrogen positive (meaning it is stimulated by estrogen) it is

difficult to know whether to recommend restricting soy. The anti-cancer effects

of soy may outweigh any possible estrogenic effects of isoflavones.

Conclusion: At this time, there seems no reason for women who have had breast

cancer to avoid moderate consumption of soy. And for women who have never had

cancer, there seems no reason to restrict soy.

 

 

 

Soy Intake and Reproduction

 

 

Scientists became aware of a potential link between isoflavone consumption and

reproductive problems because of breeding problems among female sheep that

grazed on a particular type of isoflavone-rich clover in Australia. 30 The

amounts of isoflavones being ingested by these animals were extremely high

compared to typical consumption of Asians. In addition, species vary in their

response to biologically-active compounds and sheep are especially sensitive to

isoflavones.

 

 

Although environmental estrogens, such as PCBs in fish, have been cited as

possibly lowering sperm count and possibly interfering with fertility, 31 a

recently published study showed that consumption of 40 mg of isoflavones per day

had no effect on male reproductive function parameters. 32 And while one study

has shown that soy consumption delayed ovulation in women, it did not prevent

ovulation and several other studies have not found this effect. 33 Finally, a

recent study of adults aged 20 to 34 years who were enrolled in controlled

feeding studies at the University of Iowa as infants, found no difference in a

wide range of reproductive and physiological measures between those who were fed

soy formula and those fed cow milk formula as infants. 34 There have also been

no observed widespread reproductive problems in populations where regular soy

consumption is the norm. Conclusion: Although soy isoflavones have weak

estrogen-like effects, there is no evidence of reproductive problems in those

who eat these foods.

 

 

Should You Eat Soy?

 

 

Based on the bulk of the evidence soy appears to be perfectly safe for nearly

all healthy individuals when it is consumed in reasonable amounts. We would say

that a reasonable amount of soy is two to three servings per day. Women who have

had estrogen-positive breast cancer may want to be somewhat more restrictive in

their soy intake but, if they are already eating and enjoying soyfoods, there is

not enough evidence of any harmful effects to suggest that they need to avoid

all soy.

 

 

http://www.veganoutreach.org/health/soysafe.html

 

 

About the Authors

Virginia Messina, MPH, RD is an adjunct assistant professor at Loma Linda

University and a consultant on vegetarian nutrition. Mark Messina, PhD is an

adjunct associate professor at Loma Linda University and an expert on soy and

chronic disease. He is a consultant for numerous health professional

organizations and for the soy industry.

http://www.veganoutreach.org/health/soysafe.html