The Perplexing Subject of Soy

In my preparation for today’s article on soy, I found some difficulties to approach the subject due to the controversial health issues pertaining to soy itself. Some sources have argued that soy contains certain anti-nutrients, endocrine disruptors, phytoestrogens and cancerous properties. [1] There are sources as well that rebut against some of these claims.

In this article, I’m not aiming to put my firm stand on the topic, but hopefully to showcase both sides of the argument. Soy plays a critical role in many food products such as bread, meat, ice cream and not soy milk or tofu alone. It helps to know more about the controversial issues on soy so that a better decision can be made whether to include soy in our diets or not.

(Disclaimer: I am not an expert in the health concerns relating to soy and this article acts as only a means of representing information from secondary sources. Any misrepresentation of the information here is solely my own-doing and not from the authors of the credited sources.)

Phytate (Phytic acid)

Phytic acid resides in the endosperm of the soybean, a legume and unlike whole grains which has its phytic acid stored in the bran, the phytic acid in soy may not be removed entirely during processing. The concerns of phytic acid lies primarily in its ‘anti-nutrient’ properties, by inhibiting the absorption of essential minerals such as calcium, magnesium, iron and zinc by forming a metal pytate complex with these minerals. [2]

There lies a concern for consumers of soy-based products due to the properties of phytic acid in suppressing mineral absorption, which could deplete the nourishment of soy itself. Hence, mineral supplementation may be needed in a diet with soy. Interestingly, phytic acid does hold claims of being an anti-oxidant, anti-cancerous and pro-diabetic by reducing blood sugar spikes [ibid].

Bio-availability of minerals

The bio availability of minerals here refers to the amount of minerals available to the tissues after consumption. In an experiment done by Mellanby in 1949, there were evidence showing that puppies fed a low calcium diet with phytates do develop rickets (A form of calcium deficiency), due to a decrease in the bio-availability of calcium.

Yet there was an experiment that contradict against this by indicating the presence of phytase (the enzyme that breaks down phytase) in the human digestive tract. It seems however, that fortifying phytate products with calcium can offer an alternative for calcium absorption as a mineral. [3]

There seems to be some debate with phytates effects on its absorption of magnesium as well. In a 1969 study done by McWard, chicks fed a diet containing added phytic-acid with soy experienced depressed growth due to deficiencies in magnesium despite having supplementation. In spite of this, Forbes et al concluded in 1979 that magnesium is readily available from soy products after a comparison made with soy and inorganic magnesium, in the form of magnesium carbonate [ibid].

The same controversy seems to apply for iron absorption with some research indicating that phytates hampers the absorption process while some indicating that phytates are added as a good dietary source of iron (or enhancing the process). Lastly, it appears more apparent that pytates do affect the bio-availability of zinc [ibid].


Goitrogens are chemicals that can be found in certain vegetables that can affect thyroid function in a few ways, either by interfering with certain enzymes or affecting the thyroid gland, thereby disrupting the productions of hormone productions. Goiter, the swelling of the thyroid, comes about when more hormones are needed to be produced in an already damaged thyroid. [4]

Genistein, a soy isoflavone, has been found to inhibit the active sites of thyroid peroxidases, an enzyme key in thyroid hormone synthesis. In addition, the enzyme is responsible for iodination and coupling reactions so as to synthesise certain thyroid hormones, but genistein can disrupt these processes. [5]

It seems however, that heating or fermenting soy can remove goitrogen compounds or via iodine supplementation to makeup for the interference of genistein. [4] Despite so, processed soy can still be a risk factor in developing hypothyroidism when other factors such as iodine deficiency, thyroid illnesses, environmental goitrogens or possibly age are considered.[5]

Is soy milk a healthy beverage?


Soy contains phytoestrogens, in the form of Isoflavones and are plant derived compounds that functions similarly, albeit weaker than estrogens. Estrogens are hormones that are found mainly in women and less so for men, they are responsible for certain sexual and reproductive developments. It has been understood that decline in estrogen levels can lead to hot-flashes and osteoporosis in menopausal women, while in excess, it may activate certain receptors leading to breast cancer [6].

Phytoestrogens are in the hot-seat for a long debate about its benefits and/or potential harms, it seems that the science of phytoestrogens still remain rather controversial with a lacking consensus within the scientific community about its properties in the human body. 

Likely Benefits

Soy Isoflavones had held claims of relieving menopausal symptoms such as ‘hot flashes’ and night sweats. In spite of such claims, there seems to be a weak association that soy phytoestrogens may bring any relief, likely indicating a large placebo effect. The North American Menopause Society had indicated in 2004, of insufficient clinical results to even support such claims. [7]

As for the claims in its prevention of osteoporosis, a hypothesis developed due to estrogens key role in maintaining bone density, the studies had mixed results and were weak at best. This can be due to conflicts between animal and human studies, as well as several other factors such as age or the duration of the trials [ibid].

Regarding benefits to cardiovascular health, the role of phytoestrogens in preventing heart diseases due to the reduction of LDL cholesterol are generally small and seems to apply strongly for consumers that had shifted from animal to soy protein. With that in mind, other factors such as HDL levels and blood pressure do play a part in preventing heart diseases [ibid].

Breast Cancer (Mixed of the Two)

Concerning phytoestrogen compounds and whether it helps to prevent or propagate breast cancer, there is a lacking scientific consensus in this area as well. The worry is due to the understanding that estrogens can promote the development of breast tumors [ibid].

It seems that while some studies on Asian women indicate that a higher soy consumption reduces breast cancer, the reverse was implied in studies done on Caucasian women. In dietary intervention studies, the results were generally negative while in studies done on breast cancer survivors the results were mixed as well [ibid].

It seems that more research is needed before any strong consensus can be formed, for it seems that there more factors are involved and may be even inter-linking with one another to whether soy consumption may lead to or prevent breast cancers [ibid].

Possible Concerns

The isoflavone compounds in soy taken by the mother can be passed to the fetus, with traces found in blood of the umbilical cord. The worries also stems in infants carrying 13-22,000 times the estrogen levels of their own when consuming soy infant formulas [ibid].

In a study done by North. K and Golding J on a maternal vegetarian diet during pregnancy, the results suggested that there was an increased chance of male infants having hypospadias, a deformation of the external penis, when born to vegetarian mothers. This could be due to a greater exposure of phytoestrogens.[8]

It may be likely that there are some biological effects of isoflavones in the onset of puberty for both male and female humans, due to the suggestions of animal models indicating negative effects of soy isoflavones and that their significance should be considered in critical stages during  the development of infants (e.g. pre 4 months old infants ). its hard to conclude for there are a lack of long-term studies done on human infants. [9]

Concluding Message

Mr Bean SoyMilk
Mr Bean SoyMilk

While the issues of soy in its health benefit or harm seems rather controversial, I feel that most of the concerns are due to processed soy and not fermented soy such as natto, tempeh and miso. This could be likely due to the fermenting process in removing much of these toxins.

Moreover, it seems that soy does not really have a strong impact if you are eating in moderation and functioning healthily, but it pays to be aware that there are possibilities of nutrients inhibitors, thyroid disruption or estrogen-mimicking compounds. This is crucial considering the prevalence of soy ingredients in many food products.

Caution should also be taken when consuming soy while pregnant or feeding Soy Based Infant Formula (SBIF) to infants. It is not worth risking the development of growing infants or children, especially since these changes may be permanent due to their effects on important hormones during their development.

Perhaps consulting a health-care practitioner would be wise in the absolute needing in feeding soy-based infant formulas to infants.

On a final note, I implore any readers here to discover more information regarding soy. Here are two interesting sources that I have found while writing this article.

“The Whole Soy Truth about Soy by – Kaayla T. Daniel”

Kaayla T. Daniel is the author of ‘The Whole Soy Story: The Dark side of America’s Favourite Health Food’ and holds a doctorate in Nutritional Sciences. I have yet to read her book but its interesting of the points she highlights of certain issues concerning soy. 


Further Reading

‘Linus Pauling Institute: MicroNutrient Information Center on Soy Isoflavones’ holds a very condensed article on the information regarding soy and is well worth a read. Link.



1. Kaayla.T.D,. 2016. Does Soy have a Dark Side? [online]  Available from: [Accessed 13/3/2016].

2. Curcio.P,. n.d. Dissecting Anti Nutrients: The good and bad of phytic acid [online] Available from: [Accessed 13/3/2016].

3. Reddy.N.R, Sathe.S.K, Salunkhe.D.K. 1982. Phytates in Legumes and Cereals. Advances in Food Science. Volume 28. pp. 30 – 41. [online]. Academic Press. [Accessed 13/3/2016].

4. Pick. M. n.d. Goistrogens and Thyroid Health – The Good News! [online] Available from: [Accessed 14/3/2016]

5. Deorge. D.R., Sheeman DM. 2002. Goitrogenic and estrogenic effects of soy isoflavones. PubMed [online]. Vol. 110. pp. 349-53. Available from: [Accessed 14/3/2016].

6. Pautisol. B.H., Jefferson.W. 2010. The pros and cons of phytoestrogens. PubMed [online]. 2011 Apr 12. pp 400 – 419. Available from: [Accessed 14/3/2016].

7. North. K., Golding. J. 2000. A maternal vegetarian diet in pregnancy is associated with hypospadias. The ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood. PubMed. Available from: [Accessed 14/3/2016].

8. Dinsdale C.E., Ward. E.W. 2010. Early exposure to Soy Isoflavones and Effects on Reproductive Health: A Review of Human and Animal Studies. Vol 2(11). pp 1156 – 1187. Available from: [Accessed 14/3/2016].

(Last edited 15/3/2016)



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A reused blog to record any information or lessons via self-learning.

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