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Newsletter Archive


Soy: Fact and Fiction

September 29, 2011

There are a number of anti-soy articles in fringe publications and posted on the Internet under headings such as "Soy Alert," "The Dark Side of Soy," "The Dangers of Soy," and so forth. While provocative, the assertions in these anti-soy articles are not substantiated by valid scientific research and studies published in respected journals. In an effort to support consumers who want reliable information, please consider the following point-by-point answers to the most frequent unsupported, anti-soy assertions:

Negative assertion:


Consuming soy (tofu/bean curds) as a replacement for meat and dairy products may cause mineral and amino acid deficiencies.

The research supports:


Soy protein is the only plant protein that is equivalent to animal protein. Soy foods contain all nine essential amino acids. The U.S. Department of Agriculture evaluates protein quality using the Protein Digestibility Corrected Amino Acids Score (PDCAAS). PDCAAS measures the amino acid pattern of proteins and factors in digestibility. Soy protein has a PDCAAS score of 1.0, the highest score possible, and equivalent to animal protein.

Negative assertion:


Soy damages the enzymes that manufacture thyroid hormones, as well as those enzymes essential to proper thyroid functioning. Besides this bad news, scientists have known for years that isoflavones in soy products can cause enlarged thyroid glands (goiter).

The research supports:


The data from many intervention studies reveal that soy intake does not adversely affect thyroid function in humans. In fact, a series of studies of Olympic athletes who consumed soy protein showed blood biochemistries, blood hormone levels, estrogen and thyroid hormones all remained within normal limits. A recent population-based study conducted by the Northern California Cancer Center with the University of California School of Medicine found that consumption of traditional and nontraditional soy-based foods was associated with a REDUCED risk of thyroid cancer. We are not aware of any published evidence that soy protein has an adverse effect on thyroid function in healthy humans who consume adequate amounts of iodine. Goiters are due to a deficiency of dietary iodine, not consumption of moderate amounts of soy protein as part of a healthy diet.

Negative assertion:


Diets rich in soy are high in trypsin inhibitors, which can cause pathological conditions of the pancreas, including cancer.

The research supports:


We find no published reports in the medical or scientific literature showing consumption of soy foods results in pancreatic tumor in humans. In fact, a population study showed that tofu intake is related to a lower risk of pancreatic cancer.

Negative assertion:


The amount of phytoestrogens that are in a day's worth of soy infant formula equals 5 birth control pills. Phytoestrogens can be linked with early puberty in girls and hinders physical maturation in boys. In 1998, the FDA received warnings from the British Government's final account on phytoestrogens, about their harmful reactions. FDA bureaucrats have engaged in a "rigorous approval process" for S.P.I. However, we can now protect ourselves by learning more about what's behind all these inconsistent reports as we become more aware of the health industry's claims and political propaganda concerning food supplements.

The research supports:


For 35 years, soy-based infant formula has been a safe, healthy way to support the normal growth and development of infants. The American Academy of Pediatrics endorses the use of soy-based infant formula. The results of a study conducted at the University of Iowa confirm the safety of soy-based infant formula. The study monitored the effects of soy-based infant formula on the growth and development of children and found that there were no statistically significant differences in terms of growth and development between those given soy-based formula and those fed cow's milk formula. Additionally, researchers conducted a multi-generation feeding study in rats aimed at examining the long-term health consequences of early consumption of soy protein. The number of offspring, gender ratios, birth weights, birth lengths, health, and general appearance of soy-fed rats were the same as those of milk-fed controls. On the basis of available scientific evidence, the American Academy of Pediatrics stated that soy-based infant formula is an effective alternative to breast feeding and cow-milk formula.

The negative assertion has never been observed in any study involving humans.

Negative assertion:


Phytates and soy protein reduce iron absorption so that the iron in soy foods is generally poorly absorbed.

The research supports:


In general, bioavailability of minerals from plant sources is typically lower than from animal sources. Absorption of minerals such as calcium, magnesium, zinc, copper, and iron appears to be less efficient when consumed from leguminous plants such as soybeans, but ingestion of minerals from other dietary sources concurrently with soy protein is not reduced. This observation is important because it supports the practice of mineral fortification of products containing soy protein to compensate for reduced availability of minerals naturally provided in these soy foods.

Although mineral absorption may be less efficient from soy protein sources compared with animal protein sources, overall mineral balance has not been found to be adversely compromised. Ingestion of soy protein may result in metabolic effects which could actually improve retention of some minerals such as calcium. With lower daily losses, requirements for these minerals are lower. The positive effects of soy protein ingestion on reducing mineral losses should be taken into account when the impact of soy protein on mineral status is evaluated. For example, soy protein is less hypercalciuric than animal protein and does not inhibit vitamin D activation as do phosphate-rich animal proteins. Consequently, despite a lower bioavailability of calcium from soy protein, less calcium is lost in the urine and thus mineral balance is not be adversely impacted.

Negative assertion:


In a 1996 study, researchers discovered that women who consumed soy protein isolates had a greater risk of experiencing abnormally excessive cell growth, a symptom that can be a predecessor to malignancies.

The research supports:


The 1996 study refers to the Petrakis study. This study was done with a group of women who were breast nipple aspirate fluid secretors. This study did not include a control group, and fluid secretion increased in women even after soy feeding was discontinued. In fact, a recent two-year soy intervention study showed that soy does not change mammographic densities in pre-menopausal women. An increase in mammographic densities is considered a risk factor of breast cancer.

Negative assertion:


A study called 'Dietary Estrogens Stimulate Human Breast Cells to Enter the Cell Cycle,' led researchers to conclude that women should not consume soy products, thinking that they were preventing breast cancer, when in fact dietary genistein found in soy food actually stimulates breast cell growth.

The research supports:


The study cited is just one study. Numerous other cell culture and animal studies from leading universities including Harvard University have demonstrated that genistein actually inhibits the growth of breast tumors in animals. In addition, epidemiological evidence demonstrates that consumption of soy foods may be associated with a lower risk of certain cancers - including breast cancer - in Asian countries. The death rates for breast cancer are more than 2 1/2 times higher in American women than in Japanese women. In searching for an explanation for this difference, scientists found that Asian diets tend to be low in animal protein and high in protein from soybeans and other plant sources. In fact, Asians consume 20 to 50 times more soy-based foods than Americans.

Other published studies referenced here also have found that an increase in soy consumption during adolescence results in a significant reduction in the risk of breast cancer later in life, in both pre-menopausal and post-menopausal women.

Negative assertion:


Athletes should be aware that the 'soy protein' drinks they are consuming in order to build muscle tissue may actually cause muscle protein breakdown.

The research supports:


The totality of science demonstrates that soy protein improves muscle strength and buildup. In an investigation that compared a vegetarian diet with a beef-containing diet on resistive-training-induced changes in body composition and muscle size, Dr. Haub et al found that increases in muscle strength and size are not influenced by the predominate source of protein consumed by older men with adequate total protein intake. Drs. Bordi and Cole reported that soy products support physical demands of athletes. In fact, the Nebraska Cornhuskers football team consumes soy products to improve athletic performance, and soy use has been recommended for all athletes in Nebraska. Findings from animal studies support human observations. Dr. Nikawa et al reported that diets containing soy protein prevent exercise-induced protein degradation in skeletal muscle in rats, possibly due through inhibiting the calpain-mediated proteolysis. Calpain is an enzyme that degrades proteins in skeletal muscle.

Negative assertion:

Mike Fitzpatrick, Ph.D., confirms the facts that soy consumption has been linked to disorders, such as infertility and leukemia, and that soy foods are highly estrogenic.


The research supports:


We are not aware of any data from published medical literature that links soy consumption to infertility. Strom et al investigated soy formula intake during infancy in relation to reproductive and endocrinological outcomes in young adults who consumed soy formula when they were infants. There are no significant differences between soy and cow formula groups in pubertal maturation in both sexes and pregnancy outcomes in women. It is important to note that soy has been widely used as a protein source in laboratory animal diets for medical research and we are not aware of any evidence of widespread breeding problems in laboratory animals. There is no published medical literature that link soy consumption to leukemia in humans.


Negative assertion:


Increased level of tofu consumption was found to be associated with indications of brain atrophy and cognitive impairment in later life. They even found, at autopsy, swelling of the brain cavities and a decrease in brain weight among heavy tofu eaters.

The research supports:


An analysis of 23 published studies reports that East Asian countries - which boast the highest soy consumption in the world - experience fewer incidence of dementia and Alzheimer's disease than European countries. In fact, a recent study reveals significant improvements in short- and long-term memory and mental flexibility in high soy diet users versus low soy diet users.

The researchers concluded, "Significant cognitive improvements can arise from a relatively brief dietary intervention, and the improvements from a high soy diet are not restricted to women or to verbal tasks."

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September 2005




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