Is Soy Formula Safe? An In-Depth Look at the Research


This soy formula discussion was researched and shared with us by Sarah Emerson. It’s from the March 2007 issues of Foods Matter, a vetted UK publication.

Parents may choose a soy formula for ethical or cultural reasons – or because their baby cannot be breast fed and cannot tolerate the standard cow’s milk formula.  But are they ’safe’? Following on from her investigations last month into hydrolysed and elemental cow’s milk formula, Sarah Merson now checks out the soy versions.

Is Soy Formula Safe? An In-Depth Look at the Research

Is Soy Formula Safe?

A number of infant health issues, including lactose intolerance and milk allergy, have led  parents seek out other feeding options. And where an infant has a medical reaction to other formula, soy formula is often offered on prescription.

In fact, as a result of unanswered health concerns, the Committee on Toxicity (CoT) now recommend to the Food Standards Agency that soy-based baby milks are only used when ‘indicated clinically’.  According to a report from the Scientific Advisory Committee on Nutrition (SACN), in 2003 however, there has been a steady decline in the total number of prescriptions issued for soy formula since 1994.

So, does this mean that soy formula is likely to become obsolete? We look at the background behind the health scares, and consider why soy formula should be limited to clinical use only.


Soy contains naturally occurring substances known as phytoestrogens, which have similar, though much weaker, properties to human oestrogen – the hormone involved in the development of female characteristics.

Due to their phytoestrogen content, soy-derived products have been under much scrutiny for the past 10 years. In the case of infants using soy formula, alarm bells were raised over the possibility of hormonal imbalance in early life, which could permanently affect sexual development and fertility in later life. Questions have also arisen over whether phytoestrogen intake could interfere with thyroid function in babies.

It has been acknowledged that there is no evidence to suggest that people in countries such as Japan who routinely consume large quantities of soy have reduced fertility or altered sexual development, but …

Traditional v. modern

According to CoT, processing does affect the levels of phytoestrogens in soy. Traditional fermentation reduces the levels of isoflavones two to threefold but modern factory processes do not.  Moreover, modern American strains of soy (which are often contained in baby formula as well as many other products) have significantly higher levels of isoflavones than Japanese or Chinese ones because they have been bred to be more resistant to pests. (One way to tackle pests is to stop them breeding by making them infertile. It turns out that unfermented soy did play one role in traditional Asian diets – it was eaten by monks to dampen down their libido!).

What is more, ‘Soy formula milk is a [recent]western invention. There is not the  historical evidence to show it is safe’, says Professor Richard Sharpe, head of the Medical Research Council’s Human Reproductive Sciences Unit at Edinburgh University.

Anyhow, according to Consultant toxicologist, Dr Mike Fitzpatrick who looked into the historic soy consumption in Japan and China (on which many studies are based), these populations did not actually eat that much soy and what they did eat tended to have been fermented for months.  Babies who are using soy formula, on the other hand, are consuming vast quantities.

A real risk?

On-going research still fails to give a definitive answer on whether the speculative health risks are truly valid. Adverse effects on the development of reproductive organs and fertility have been reported in animals after administration of large doses of phytoestrogens. However, there is no evidence of similar effects in humans. Nonetheless, the DoH’s, Committee on Toxicity (CoT) has concluded that there is evidence of potential risk and has recommended to the Food Standards Agency (FSA) that soy-based baby milks are only used when ‘indicated clinically’.

Prescription only?

In reality, this would mean a necessary change in the marketing of soy formula so that they become a prescription-only item. This would prevent off-the-shelf purchases and parents using them without having discussed it first with a health professional.

Moreover, because so little is still known about the effect of soy on young infants, all infants using it should, ideally, be monitored.  This would be much easier if the product was only obtained on prescription. The FSA are yet to take this action.

Shared allergenicity

A joint statement by the European Society for Allerology and Clinical Immunology (ESPACI) and the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) recently highlighted another reason to reduce the use of soy formula in the treatment or prevention of cow’s milk allergy.

According to the ESPGHAN, prospective studies have shown that soy formula are as allergenic as conventional cow’s milk based formula. They therefore suggest that they should not be recommended for the prevention of food allergy. Further studies however, are be required.

The ESPGHAN committee concluded that:

  • infants with cow’s milk protein allergy who are not breast-fed should receive ‘extensively’
    hydrolysed protein from cow’s milk or, in selected cases, a product based on an amino acid mixture.
  • Bottle-fed infants with a documented hereditary risk of allergy should be exclusively fed a formula with a confirmed reduced allergenicity which may reduce the incidence of adverse reactions to food, especially cow’s milk protein.
  • Exclusive breastfeeding during the first 4-6 months might greatly reduce the incidence of allergy and is strongly recommended.

Reducing phytoestrogens

None of the soya available to the industry is naturally low in phytoestrogens and therefore the only option is to reduce the levels by processing. This is exactly what the government urged manufacturers to do in 1996.

The Food Commission, in their own 1998 investigation,found that companies had failed to respond to this demand and that they ‘blocked direct enquiries’.

More recently however, suppliers of soy protein isolate, used in the manufacture of soy formula, have been investigating means of reducing phytoestrogen levels. One major company is looking at the possibility of using a non-solvent extraction procedure although the work is still at an early stage. An infant formula manufacturer in the USA is also investigating the use of an ion exchange method to reduce levels.

The formula manufacturers have pointed out that it is important that any new process does not affect the nutritional quality of the final product as any significant change would require its re-assessment by relevant expert committees.

About Author

Alisa is the founder of, Food Editor for Allergic Living magazine, and author of the best-selling dairy-free book, Go Dairy Free: The Guide and Cookbook for Milk Allergies, Lactose Intolerance, and Casein-Free Living, and the new cookbook, Eat Dairy Free: Your Essential Cookbook for Everyday Meals, Snacks, and Sweets. Alisa is also a professional recipe creator and product ambassador for the natural food industry.

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