Questions and anwers on consuming soy products

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Is Soy Safe?

Q & A with Brenda Davis, R.D.

Q: Is Soy Dangerous?

 

Q: I've been reading quite a bit about the dangers of

consuming too much soy, but to date I have not figured

out what those dangers are other than too much

estrogen production with its consequences for higher

cancer risk. A friend told me that a woman with a

Vegetarian Nutrition course to her credit told her

that she would recommend rice beverage over soy. Why?

Would you kindly clarify this matter for me.

 

Thanks,

Joyce Ward, Winnipeg

 

 

A: Dear Joyce,

 

Thank you for the opportunity to provide some clarity

about this issue. As you may be aware, soy has enjoyed

considerable favourable press over the past decade. We

have seen reports of soy reducing risk of heart

disease, cancer, osteoporosis, and reducing symptoms

of menopause. Just when soy seemed to be on top of the

world, articles and websites began to appear claiming

that this new-found health hero was really a villain

in disguise. Soy bashers said all the hype about soy

was really just propaganda, and that in truth, soy was

not a health food, but rather a dangerous substance

that should be carefully avoided by humans. In fact,

anti-soy advocates claim that eating soy raises risk

of cancer, osteoporosis, thyroid problems, birth

defects, reproductive problems, nutritional

deficiencies and Alzheimer's disease. This has left

consumer wondering if soy is really a saint or a

sinner.

 

First, it is important to understand that soy is not

something new. The soybean has been used for food for

centuries, particularly in the Orient. Traditional

forms of soy foods included fresh or frozen beans from

the soy pod (called edamame ), soy milk, tofu, and

fermented foods, such as tempeh, miso and soy sauce.

More recently soy has become a huge hit in North

America, with all of the traditional forms of soy

widely available in addition to numerous others, such

as soy nuts, soy-based meat analogues, soy-based

protein beverages, soy chips, soy ice cream, soy

yogurt, and the list goes on. These products have

become staples for many vegetarians and vegans. So,

the question of the safety of soy is one that

certainly deserves serious consideration.

 

Let's briefly address a few of the major claims

against soy. For more detailed information about each

of these issues, the following websites are most

helpful:

 

www.llu.edu//llu/vegetarian/soy2.html

www.foodrevolution.org/what_about_soy.htm

www.soybean.com/drsuz.htm

 

Soy and Breast Cancer

 

Claim : Soy increases risk of breast cancer.

 

Among the very first health claims made for soy is

that it may reduce incidence of breast cancer. It

seemed so obvious when one compared the very low rates

of breast cancer in Asian countries using large

amounts of soy with rates in North American countries

that used comparatively small amounts of soy. The risk

reduction was thought to be due to the isoflavones

(mainly genestein and daidzen) in soy. Isoflavones are

a type of phytoestrogen (plant estrogen) that has been

thought to interfere with the ability of the potent

human form of estrogen to increase cell proliferation

and, therefore, cancer risk. However, studies have

been mixed. While some do indeed show soy acting as an

anti-estrogen, others suggest soy may act as a weak

estrogen itself, increasing cancer risk.

Interestingly, some studies have shown that while

small amounts of genestein increase cell growth, large

amounts inhibit it. Finally, there is some evidence

that women eating soy from an early age (especially

during puberty) do reduce their breast cancer risk,

while there seems to be less protection for those who

begin to eat soy later in life.

 

Conclusion: We still do not know all the answers where

soy and breast cancer are concerned. However, the

evidence is sufficient to say that soy consumption

does not increase risk of breast cancer and may reduce

risk in some people, especially if soy is consumed

from an early age. For those who have

estrogen-positive breast cancer, it also appears safe

to use soy in moderation.

 

Soy and Thyroid

 

Claim : Soy contains natural chemicals known as

goitrogens that interfere with thyroid function. These

can cause an enlargement of the thyroid gland (a

“goiter”) and symptoms of hypothyroidism, such as

lethargy, dullness, coldness, and depression.

 

It is true that soy contains goitrogens, as do many

other foods such as cruciferous vegetables (cabbage,

cauliflower, broccoli, and brussel sprouts), sweet

potatoes, lima beans, and millet. However, these foods

have been found only to cause problems when iodine

intake is low , because goitrogens do their damage by

interfering with the thyroid gland's ability to

utilize iodine. Between 1951 and 1961, several cases

of goiter were diagnosed in infants who had been fed

infant formula made from soy flour. These cases are

frequently cited by the anti-soy lobbyists to prove

soy damages thyroid function (especially in infants).

But not a single case of goiter in infants has been

caused by soy formula since the 1960s. At that time

the soy formula base was changed from soy flour to soy

protein isolates, which are low in goitrogens, and

manufacturers began fortifying soy formula with

iodine.

 

Soy does not cause thyroid problems in healthy,

well-nourished people who are not deficient in iodine.

However, people who do not have a reliable source of

iodine could increase their risk of thyroid problems

if they eat a lot of soy and/or other foods rich in

goitrogens. Iodized salt, dairy products, and fish are

the main dietary sources of iodine, and most

multivitamin/mineral supplements provide the

recommended daily allowance. So the answer is not to

avoid soy or cruciferous vegetables, but to get enough

iodine.

 

Conclusion : There is no evidence that eating soy

foods regularly causes thyroid problems in healthy

people who include sufficient iodine in the diet.

 

Soy and Cognitive Function

 

Claim: Soyfoods, especially tofu, can cause mental

deterioration and accelerate aging.

 

One study done in Hawaii (the Honolulu Heart Study)

found that Japanese-American men who ate the most tofu

in middle age had the greatest mental deterioration

and dementia as seniors. This study is widely cited as

evidence that tofu may cause a reduction in cognitive

function. Interestingly, there have been at least

three other studies that have suggested that soy

provides significant beneficial effects on cognitive

function. In addition populations with relatively high

soy intake (about a serving a day), including people

in Asia and Seventh-day Adventists, experience lower

rates of dementia than those populations who eat

little if any soy. While this does not prove that soy

is beneficial, it does suggest that moderate soy

consumption is likely not detrimental.

 

Conclusion. The weight of the evidence suggests that

soy may offer some benefits to cognitive function,

although more research is needed before firm

conclusions can be made on this issue.

 

What about soy versus rice milk? It all depends. If

you are sensitive to soy or use a lot of soy products,

you may wish to use fortified rice milk. However, my

preference is for soy – especially for children. Soy

is a much richer source of high quality protein,

vitamins and minerals. It also contains isoflavones,

which are protective for heart health and against

osteoporosis. I think it tastes better too.

 

Brenda Davis is a registered dietitian in Kelowna,

B.C., a globetrotting lecturer and the author of

several books, including Why Vegan and The New

Becoming Vegetarian .