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Is soy formula safe for my vegan baby?

Alina Petre, MSc. RD.

As a vegan parent-to-be looking into feeding options, I came across a ton of information suggesting that soy formula is bad for babies.

Sure, I had planned on breastfeeding. But what if, for one reason or another, it was not possible? Would I be negatively impacting the health of my child by choosing a soy formula?

Luckily, I was able to breastfeed my baby. So this was not a topic that I ended up stressing about while adjusting to motherhood. But this topic has been on the back of my mind so I’m glad to have finally found the time to take a good look at the research.

This article reviews the latest studies to determine whether soy infant formula is a safe choice for vegan babies.

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Table of contents

Human milk is generally considered the best nutrition choice for human babies.

For this reason, health organizations typically encourage women to exclusively breastfeed for the first 4-6 months, and continue to do so while introducing solids for at least the first year (1, 2, 3, 4). 

However, it’s important to acknowledge that breastfeeding isn’t always feasible. Formula is designed as a suitable alternative and delivers fluid, protein, carbs, fats, vitamins and minerals in ratios appropriate for a baby’s growth and development  (5, 6, 7).

Soy formula is a popular alternative for vegan parents. Aside from its lanolin-sourced vitamin D, it’s exclusively derived from plants. Hence, many vegan parents prefer it for ethical, environmental or health reasons. 

Nowadays, you can even find a few vegan baby formula brands that are 100% vegan.

Interestingly, soy formula is a popular choice with a proportion of non-vegan parents as well. These parents may prefer it over cow milk-based formula for medical reasons, allergy or tolerance issues or in the hope of reducing their baby’s risk of disease later in life.

IN SUM – Soy formula provides a suitable alternative in cases in which breastfeeding is not feasible, especially for vegan babies, or those with certain allergies, intolerances or other medical issues.

Is soy formula as good as other types of baby formula?

All baby formulas available on the market are required to go through a thorough regulatory process and meet certain criteria in terms of composition and final nutrient content (8, 9).

This ensures that all baby formulas are equally able to meet the average baby’s nutrition needs, regardless of whether they’re made from soy or cow’s milk. 

Please note that cow milk, plant milks or homemade baby formula aren’t appropriate for babies under the age of one. That’s because they contain a suboptimal ratio of protein, carbs and fat and lack iron and other nutrients important for a baby’s development. 

If breastfeeding isn’t feasible, or is stopped before one year of age, infants would benefit from receiving an iron-fortified infant formula until their first birthday. 

IN SUM – All baby formulas available on the market undergo a thorough regulatory process that ensures they adequately meet the average baby’s nutrition needs.

Should vegan children continue to drink formula until they’re 2 years old?

Some healthcare providers view plant-based beverages as nutritionally inferior to homogenized (3.25% M.F.) cow’s milk. Because of this, they recommend that vegetarian and vegan families give their children soy formula until they turn two years old (1).

This may be a cautious way to ensure that toddlers meet their nutrition needs despite bouts of picky eating.

Some plant-based milks contain less protein, fat, calcium, vitamin D, and iodine than dairy milks. Soymilk contains roughly the same amount of protein as cow’s milk. Meanwhile, fortified plant milks contain the same amount of calcium, vitamin D and iodine as cow’s milk.

In addition, plant milks aren’t the only way to get the nutrients found in cow’s milk. For instance, foods like avocados, olives, coconut, nuts, and seeds are great ways to ensure your child gets enough fat in their diet.

All this to say that if your child’s overall diet is well-balanced and provides the nutrients found in cow’s milk from other sources, formula may not be necessary until your toddler’s second birthday.

When in doubt, consider discussing your own specific circumstance with a registered dietitian specializing in plant-based diets. If you don’t have easy access to one, feel free to contact me – I do advise families remotely.

You can find more in-depth information on the nutrients of concerns for vegan children, and when it may be important to supplement them in this Dietitian’s Guide to Vegan Supplements for Kids.

IN SUM – Some experts recommend that vegan toddlers continue to drink formula until their second birthday. Discuss what’s best suited for your specific circumstances with a specialized registered dietitian. 

The soy formula controversy

Soy baby formula is often the source of controversy. Let’s discuss the main points parents tend to be concerned about.

Why are people concerned about soy formula?

People generally express concern about soy formula for the following reasons:

It’s noteworthy to mention that despite these potentially concerning factors, most studies fail to observe any significant long-term differences in growth, development or overall health between cow milk formula-fed and soy formula-fed babies (12, 13, 14).

Does soy formula contain estrogen?

Soy is rich in isoflavones, a category of compounds naturally found in all beans, including soybeans. 

Soy isoflavones are commonly referred to as phytoestrogens, or plant estrogens. This is because their structure resembles that of the reproductive hormone estrogen that’s naturally present in the human body. 

Due to their similarity in structure, soy isoflavones can attach to estrogen receptors in the body. Some fear this will cause estrogen-like effects at a time in a baby’s development when exposure to estrogen is typically low.

However, soy isoflavones differ from estrogen in a few ways. 

For instance, soy isoflavones cannot bind to some types of estrogen receptors and must compete with estrogen to actually bind to the others. As a result, they are 1,000 to 10,000 times less likely to activate estrogen receptors when compared to estrogen (12, 13).

In fact, it’s estimated that only 0-3% of a baby’s blood isoflavone levels are actually active (15).  

This is why experts consider that soy isoflavones are unlikely to have strong estrogen-like effects in humans (12).

Is soy exposure riskier in babies?

A baby’s diet relies exclusively on breastmilk or formula in the first few months of life. In most cases, these will continue to make up a big part of a baby’s diet, even once solids begin being introduced.

This means that babies fed soy formula are typically exposed to larger amounts of soy isoflavones than breastfed babies or those fed cow’s milk formula. 

Soy formula-fed babies are also likely to consume larger amounts of soy isoflavones than toddlers or adults, who eat soy as part of a more diverse diet (16).

Infants grow at very fast rates and go through developmental stages that are particularly sensitive to estrogen. Accordingly, some people worry that soy isoflavones may pose a higher risk to babies than to other age groups.

Despite this worry, studies typically fail to find any lasting or significant negative effects in adults who were fed soy formula as babies (12, 13, 14).

Again, it’s important to keep in mind that soy isoflavones are much less potent than estrogen and that only 0-3% of the circulating isoflavone levels measured in infants fed soy formula are actually active (12, 15).

So while valid on paper, these worries don’t seem to translate to real-life problems.

IN SUM – Soy formula contains higher amounts of aluminum, phytates and isoflavones than breastmilk or cow milk formula. Some worry this may cause reproductive and long-term health problems.

Potential dangers of soy formula

Concerns about the effects of isoflavones on the reproductive health of animals date back more than 50 years ago. This is when it was first noticed that sheep and cows grazing on red clover — a rich source of isoflavones — were infertile (17, 18).  

Since then, several animal studies have researched the effects of isoflavones on reproductive and general health. Here’s a summary of the most prominent concerns raised:

How does animal research apply to humans?

These concerning studies have rightfully sparked debate.

That said, it’s important to note that results of animal studies are not easily applicable to human babies, for a number of reasons.

For starters, animals, metabolize isoflavones very differently than humans do. This is even true for monkeys, which most people assume are quite similar to humans (15).

Moreover, animals are often given an isolated component of soy formula, such as one soy isoflavone, rather than soy formula as a whole. Effects are likely different when isoflavones are given in an isolated manner rather than as part of a whole mix. 

Finally, animals are sometimes exposed to higher doses of soy isoflavones, for longer periods of time or receive isoflavones through intravenous injections – all of which greatly differ from what happens with babies (12, 15).

Therefore, despite what flashy headlines may have you believe, it remains difficult to extrapolate results from animal studies and apply them directly to humans. 

IN SUM – Soy isoflavones have been linked to a range of reproductive and health abnormalities in animals. However, results from animal studies are likely not fully applicable to humans.

Is soy formula harmful to human babies?

Unlike animal studies, human studies measuring both the short-term and longer-term impact of soy formula generally find little to no negative effects.

When negative effects are identified, they appear to have a minor significance (12, 26, 27, 28, 29).  

Let’s address each of the initial concerns related to soy baby formula one by one.

High aluminum content

The aluminum content of soybeans is an often-cited reason for concern. These higher levels may have negative effects on brain and bone mass development (10).

Soy baby formula contains up to 50 times more aluminum than breastmilk or cow’s milk baby formula. The concern is that these higher levels may have negative effects on the brain and bone mass development of babies (30).

However, despite the difference in aluminum content, a 2019 study reports no differences in blood aluminum levels in children fed soy versus cow’s milk formula (31).

It seems that 95% of the aluminum from soy formula is not absorbed in the gut. Moreover, the 5% that is absorbed appears to be excreted by the kidneys (31).

The current data suggests that soy-based formulas are well-tolerated and result in normal growth and nutritional status in healthy babies (32).

High phytate content

Soy is naturally rich in phytates. Phytates are a plant compound that can reduce the body’s ability to absorb nutrients. This causes some to worry that soy formula-fed babies will receive insufficient nutrients, which can affect their growth and development (11).  

Old soy formula formulations used to contain phytates. However, phytates appear to be almost totally removed from modern soy formula (33).

Historically, soy baby formula also lacked appropriate quantities of certain amino acids, and were deficient in iron, zinc, calcium and phosphorus. This, rather than its phytate content, could be the main reason why soy formula-fed babies received fewer nutrients.

However, this is no longer the case in modern formulations, which are supplemented with appropriate levels of nutrients (33).

Recent studies are unable to see a link between soy-based infant formula and growth parameters. This suggests that the phytate content of soy baby formula is likely a non-issue (26, 30, 34).

High isoflavone content

Soy formula is naturally rich in isoflavones, a plant compound resembling the hormone estrogen. Some fear that soy isoflavones may negatively impact a baby’s reproductive system or long-term health (12).

One often-cited study related to these concerns dates from 2014.

The review looked at studies published up to mid-2013. It reports that girls exposed to soy isoflavones during pregnancy and early life may have more breast tissue. They also appear to get their menses earlier and experience longer and more painful periods (26).

However, when I looked at the data closely, I only noticed modest differences.

For instance, menses began, on average, only 5 months earlier and lasted only 9 extra hours. Moreover, the period pain was rated as only slightly higher in women who were fed with soy formula as babies.

Similarly, the differences in breast tissue were minimal. The researchers further explained they believed that these differences may be caused by baby breasts taking longer to wane rather than an increase in breast tissue per se.

This study review is often cited as a strong reason to be concerned about soy baby formula. Yet, in my opinion, the negative effects described, although statistically significant, don’t appear to have strong real-life significance.

Moreover, no differences in growth, brain function, bone, metabolic, reproductive, hormonal, immune health were found between babies fed soy formula, cow’s milk formula or breastmilk (26).

In addition, three more recent studies report no link between soy baby formula and the early onset of puberty (30, 34, 35).

Does soy formula affect thyroid function?

Another often-cited concern is that soy formula may interfere with the proper function of the thyroid gland.

There are few studies on this topic in children. Most are case reports dating back to the 1960s, before iodine was routinely added to soy baby formula (12).

Modern studies report that soy formula isn’t a cause of concern in babies with a healthy thyroid gland (12, 13, 14). However, it may interfere with the absorption of thyroid medication.

Therefore, children with hypothyroidism fed soy baby formula should be closely monitored so their thyroid replacement medication can be adjusted accordingly, if need may be (12).

Genetically modified soy in baby formula

A true problem to consider is the use of genetically modified soy in making soy baby formula.

According to the U.S. Department of Agriculture (USDA), 93% of soybean crops are genetically modified.

The European Academy of Allergy and Clinical Immunology (EAACI) and the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) worry that genetically modified soy is less nutritious, less likely to be easily digested, and more likely to cause an allergic reaction (31).

Because of this, they recommend not giving soy during the first 6 months of life, and to children who have digestive issues (31).

To counteract this worry, you could opt for a soy baby formula that is organic and GMO-free.

Other potential negative effects to consider

New studies on this topic are continuously emerging. A handful of them link soy formula to an increased likelihood of period pains, heavy bleeding, endometriosis or uterine fibroids (36, 37, 38, 39).

However, more studies are needed to confirm these effects, including their real-life significance.

Another study suggests that baby girls fed soy formula in the first 9 months of life may experience changes in vaginal cells and differences in how specific genes get turned on or off when compared to babies fed cow milk formula (32).

However, it remains unclear whether these differences have any short or long-term health effects.

IN SUM – Most of the concerns linked to soy baby formula aren’t strongly supported by current scientific data. Two concerns you may want to truly consider are soy formula made from genetically modified soy, and using soy formula with babies with hypothyroidism.

When should you avoid soy formula?

Soy formula is generally considered a safe choice for most vegan babies.

That said, soy formula may not be the best choice for babies born prematurely, or for those with certain medical conditions, allergies or intolerances (30, 40).  

Parents of babies fitting these special cases should seek guidance from their healthcare provider when attempting to choose the baby formula most appropriate for their baby’s needs.

Moreover, although soy formula appears to have no negative effect on babies with a normally functioning thyroid gland, it may reduce the absorption of thyroid hormone medication in those who require it (12, 15, 41).

Thyroid levels can be closely monitored and medication levels adjusted accordingly, even in babies fed with soy formula. However, parents should discuss the feasibility of this option directly with their healthcare provider.

Finally, it may be wise to avoid soy formula made from genetically modified soybeans until more data is published concerning its safety (31).

IN SUM – Soy formula is generally considered safe. Parents of babies born prematurely or with certain medical conditions should discuss the formula best suited for their baby with their healthcare provider.

To sum it all up

The safety of using soy formula to feed babies is a controversial topic.

Yet, despite concerns about its composition and negative effects in animals, most human studies to date report little to no long-term negative effects in humans.

That said, soy formula may not be the best choice for premature babies, or those with allergies, intolerances or specific medical conditions. 

All-in-all, research is only meant to offer some guidance. As a parent, it remains up to you to weight the pros and cons to reach the decision that best suits your family.

When you’ll be ready to introduce solids, download a free copy of the 76 best first foods for vegan babies below. Then simply pick a food from each category when building your baby’s meals.

Pin it this list to your board for easy access when your little one is ready for solids!
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