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The Soy Controversy by Mary G. Enig, PhD

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This article summarizes a presentation given on May 25, 2001 at the 8th International Symposium of the Institute for Preventive Medicine in Vancouver, Canada.

Promotion of soy foods as a replacement for animal foods such as eggs, fish, meat, milk and poultry in the diets of men, women, children and infants in the US is being aggressively pursued by the government (the US Food and Drug Administration18), by individuals (authors Stephen Holt25,26 and Mark Messina34,35), and industry (American Soybean Association and Protein Technologies International, a division of DuPont). In addition, the pharmaceutical industry and major health food companies are promoting the fractionated phytoestrogens or isoflavones isolated from soy as a desirable treatment for peri- and postmenopausal women, as appropriate treatment for various hormone-based cancers, for hot flashes and to prevent osteoporosis.

At the same time, a number of scientists and writers have issued warnings53 about the adverse effects of soy, citing both the scientific literature dating back over 60 years as well as recently published studies. Most prominent among those raising concerns are Richard and Valerie James8,50 and toxicologist Mike Fitzpatrick16 in New Zealand; journalists Sue Dibb and Lynn McTaggart in Britain; and Sally Fallon and Mary Enig of the Weston A. Price Foundation in the US.15

This report will examine some of the claims made for soy, with emphasis on studies published within the last twelve years.

Soy usage in Asia

Soy proponents claim that soy is a staple in Asia. A "staple" is defined as a major commodity, one that provides a large portion of calories in the diet. Actually, overall consumption of soy in Asia is surprisingly low - it is not a staple like rice, fish or pork.

The famous Cornell study of diet in China, conducted by T. Colin Campbell, found that legume consumption ranged from 0 to 58 grams per day, with an average of about 13 grams.5,7 Assuming that two-thirds of this is from soybeans, this translates to about 9 grams (less than 2 teaspoons) of soy on average, with a high of about 2 tablespoons. [A 1975 book on nutrition published by the California Department of Health lists soy foods as minor sources of protein in Japanese and Chinese diets.41 Major sources of protein listed were meat including organ meats, poultry, fish and eggs.]

Soy is a condiment in Asian diets, not a staple. No one would call mustard a staple in the American diet even though it is a very typical foodstuff.

On October 26, 1999, the FDA authorized the use of a health claim for soy protein.18 The regulations stipulate that 25 grams of soy protein per day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. Soy foods that contain at least 6.25 grams of soy protein per serving may make a Soy Health Claim. The rationale for this regulation is that Asians consume about 25 grams of soy protein per day and Asians have low rates of heart disease. Yet a study of Japanese men and women conducted in 1998, just one year before the FDA ruling, found that the average consumption of soy products was about 54 grams per day for women and 64 grams for men.36 The total amount of soy protein from these products was 7-8 grams.

Twenty-five grams of soy protein per day, the amount recommended by the FDA, provides about 75 mg or more of isoflavones, the estrogen-like compounds in soy. By contrast, the typical Japanese diet contains one-third as much. Total isoflavones in the 1998 dietary survey was about 25 mg.36 This is in line with a study published in 2000 giving about 28 mg isoflavones per day.37 A 1996 study found that consumption of isoflavones in Japan was considerably less, averaging about 10 mg per day.22

Soy usage in animal diets

Pigs have a digestive system similar to humans. Dietary mixtures for pigs - which are carefully formulated to promote reproduction and growth - allow approximately 1 percent of the ration as soy in a diet based on grains and supplements.4 The Central Soya Company, Inc. website gives a range of 2.5 percent to 17.5 percent soy in the diet of pigs, citing a number of anti-nutritional components that "have been documented to cause gastrointestinal disturbance, intestinal damage, increased disease susceptibility and reduced performance in pigs."

In recent studies, rats fed the isoflavone genistein exhibited pathological changes in the colon23 and rats fed soy-based chow had reduced growth and an increase in gastrointestinal problems.40

Soy and Osteoporosis

Many publications claim that soy foods can protect against osteoporosis. In one recent study, soy consumption seemed to attenuate bone loss from the spine in premenopausal women when measured by dual energy X-ray absorptiometry.1 However, in another study, soy did not prevent bone loss when measured at autopsy in female monkeys who had had their reproductive organs removed.9

Soy and coronary heart disease

Claims that soy can prevent heart disease are based on the fact that soy consumption appears to lower so-called bad LDL and raise so-called good HDL.3,10,11,38,44 This hypothesis is dubious. Ravnskov and others have pointed out that serum levels of HDL and LDL are not good predictors of proneness to heart disease.46 [In fact, research indicates that high levels of HDL are an indication of thyroid problems.42 If this is so, higher levels of HDL after consumption of soy would tend to confirm soy's known antithyroid effects. Soy's effect on the thyroid gland "bounces all over the place," meaning that it can have repercussions on many different functions in the body.]

However, elevated levels of a substance called Lp(a) do provide an accurate marker for proneness to heart disease. In a recent study, consumption of soy was shown to raise levels of Lp(a).39

Soy and female hormone replacement

Soy promotion efforts have targeted women who are concerned about the side effects of hormone replacement therapy (HRT).12, 14, 33 Yet a study published in November 2000 concluded that "Current data are insufficient to draw definitive conclusions regarding the use of isoflavones as an alternative to estrogen for hormone replacement in postmenopausal women."52

In premenopausal women, significant changes in hormonal patterns and length of menstrual cycle were observed when 60 grams of a special soy protein containing 45 mg isoflavones was given daily for one month.6 The changes were similar to those observed in women taking tamoxifan and indicate that soy foods have the potential to disrupt the endocrine system.32 In another study, soy consumption increased sex hormone-binding globulin (SHBG) levels in postmenopausal women, which is further evidence of endocrine disruption.43

A study published March 2000 found that soy did not relieve hot flashes in breast cancer survivors.45

Soy consumption and Thyroid function

Studies indicating soy's antithyroid effects go back almost 60 years and continue to the present. A report in Pediatrics 1995 described a case of persistent hypothyroidism in an infant who had received soy formula.8 A 1990 study documents the association of soy formula feeding in infancy and autoimmune thyroid problems.20 A 1991 study in Japan found that soy consumption can suppress thyroid function and cause goiters in healthy people, especially elderly subjects.29 In rats, excess soybean intake with iodine deficiency caused abnormal growth of the thyroid gland.27

In 1997, scientists Divi, Chang and Doerge of the National Center for Toxicological Research discovered that the antithyroid components in soy were the isoflavones that the industry promotes as panaceas for osteoporosis, heart disease and problems associated with menopause.13 Low thyroid function can contribute to osteoporosis, heart disease and problems associated with menopause.

Soy in infant diets

An important study by Setchell,48 published in 1997 in The Lancet and reported elsewhere in the scientific literature,28,49 determined that infants fed soy formula received 28-47 mg of isoflavones per day. Said the authors: "The daily exposure of infants to isoflavones in soy infant formula is 4-11 fold higher on a body weight basis than the dose that has hormonal effects in adults consuming soy foods. Circulating concentrations of isoflavones in the seven infants fed soy-based formula were 12,000-22,000 times higher than plasma oestradiol concentrations in early life, and may be sufficient to exert biological effects, whereas the contribution of isoflavones from breast-milk and cow-milk is negligible."48

Soy formula fed to premature babies caused an increase in digestive enzymes compared to milk-fed babies, indicating low digestibility of soy formula.31 Another study found that twice as many soy-fed children developed diabetes as those in a control group that was breast fed or received milk-based formula.19

Even more disturbing is the evidence for endocrine disruption found in the study of premature thelarche in Puerto Rico.21 Soy infant feeding was associated with higher rates of early development in girls - including breast development and pubic hair before the age of eight, sometimes before the age of three.

It is well known that soy has adverse effects on animal reproduction. A study on rats found that soy feeding caused "subtle alterations in some sexually dimorphic behaviors."17 In other words, the differences between males and females were less pronounced than normal.

Another study found that exposure to the isoflavone genistein in pregnant rats caused changes indicative of later breast cancer in the offspring.24 Isoflavones have been shown to exert an estrogenic effect on the male mouse reproductive tract.2,51

In males, exposure to phytoestrogens alters sexual differentiation and is associated with an increasing incidence of disorders of the reproductive organs.47 Vegetarian mothers exposed to high amounts of phytoestrogens during pregnancy have a fivefold greater chance of giving birth to a baby boy with hypospadias, a birth defect of the penis.40


An alliance of government, industry and media is heavily promoting soy foods for a variety of conditions including prevention of breast cancer, prevention and treatment of osteoporosis, treatment for prostate cancer, and as a cholesterol-lowering agent for the prevention of coronary heart disease. Consumers are told that soy can provide adequate protein for vegetarians, that it is a healthy substitute for meat and milk for those who believe they should avoid saturated fat, and that it can be used to feed infants who are said to be lactose intolerant. Soy is a staple in China and Japan, say the columnists, and we need the protection it affords.

What the industry needs is a market for its surplus of soy protein isolate (SPI), which is a by-product of the soy oil industry. Industry food technicians have spent the last 40 years developing palatable products from the unappetizing high-protein slush left after soy oil is squeezed out of the beans. It is the demand for vegetable oils used in convenience foods that has stoked the rapid growth of soy production, from 18.9 million acres in 1954 to 72 million acres in 1998, not any grass roots demand for soy foods. Today soy protein isolate forms the basis of a $1.6 billion market of imitation foods - from tofu burgers to soy milk - purchased by consumers who have accepted the fallacy that traditional foods are bad for them and must be avoided.


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Sidebar articles

Soy Damages

If you believe that you or a family member has incurred reproductive or thyroid damage due to ingestion of soy foods or soy infant formula, please contact Roger Chapman, Esq. of Johnston Lawrence in New Zealand, who is collating a list of victims in preparation for a class action lawsuit. Send your confidential information to PO Box 1213, DX SP 20004 Wellington, New Zealand or

Unsubstantiated Claims

Stephen Holt, an MD specializing in gastroenterology, has written two influential books on soy (Soya for Health: The Definitive Medical Guide and The Soy Revolution) in which he makes a number of untenable claims:

CLAIM: Soy protein is a complete protein with a value "similar to . . . animal proteins, such as cows milk protein."

FACT: Compared to cows milk protein, which has a Protein Quality Score (PQS) of 100 percent, soy milk has a PQS of 40 percent due to low levels of methionine and cysteine. (Holt admits that soy is low in methionine but discounts the importance of methionine.)

CLAIM: Phytoestrogens (isoflavones) are ubiquitous in the diet and there is no evidence of their toxicity.

FACT: Toxicity of isoflavones is well documented in humans and animals. Holt admits that "soy isoflavones have 'bothered' some male athletes." Soybeans have higher levels of phytoestrogens than most other legumes commonly consumed.

CLAIM: Asians can consume 100 mg or more of isoflavones daily from dietary sources, so taking 50 to 100 mg of isolated isoflavones is very safe for most people.

FACT: Isoflavone levels reported in Japanese scientific literature appear to be in the range from 28 mg downward. The amounts consumed in China are less. Daily intake of 45 mg for one month caused hormonal changes in women.6

Phytoestrogens in Diets of Infants and Adults

  Average Isoflavone
Daily Intake
Isoflavone Intake
per kg of Body Weight
Japan (1996 survey)22 10 mg 0.17 mg
Japan (1998 survey)36 25 mg 0.42 mg
Japan (2000 survey)37 28 mg 0.47 mg
In American women, causing hormonal changes after 1 month6 45 mg 0.75 mg
FDA recommended amount 75 mg 1.25 mg
In children receiving soy formula48 38 mg 6.25 mg

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