Is Soy Formula Safe for Your Baby?

Soy formula is an increasingly popular alternative to cow’s milk formula.

Some parents prefer it for ethical or environmental reasons, while others believe it may reduce colic, prevent allergies, or reduce their child’s risk of disease later in life (1, 2, 3).

However, the use of soy formula comes with a few risks and may not be a safe feeding option for all babies.

This article reviews the latest research to determine whether soy formula is safe for your baby.

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How does soy formula compare with other formulas?

All baby formulas are required to fulfill certain criteria regarding their composition, purity, and nutrient content (4, 5).

This regulatory process helps ensure that all baby formulas meet a baby’s nutritional needs, regardless of what they’re made from.

As such, soy formulas contain the same amount of calories and important nutrients as other types of baby formulas. Therefore, they have the same ability to meet a baby’s growth and developmental needs.

The nutrition composition and safety of baby formulas are strictly regulated. This ensures that all formulas on the market, including soy formulas, equally meet a baby’s growth and developmental needs.

Does soy formula provide any health benefits?

Some parents who prefer soy formula believe it’s the most beneficial choice for their child’s current and future health.

This belief may stem from studies linking soy-rich diets to a lower risk of certain diseases, including type 2 diabetes and heart disease in adults (6, 7, 8, 9).

However, there’s currently insufficient evidence demonstrating that soy formula use in infancy reduces a baby’s risk of developing these diseases later in life (1, 2, 3).

Similarly, there’s no strong evidence that soy formula reduces digestive issues like colic or offers any additional protection against allergies. Therefore, more research is needed before strong conclusions can be made (3, 10).

On the other hand, experts agree that soy formula is the most appropriate choice for full-term babies with galactosemia or hereditary lactase deficiency — two medical conditions that prevent babies from breaking down the natural sugars in cow’s milk (1, 2).

Soy formula is also the most appropriate choice for vegan families. Although the vitamin D3 in most soy formulas is currently sourced from sheep lanolin, they’re the closest available option to fully vegan baby formula.

Many believe that soy formula use in infancy reduces colic, allergies, and the risk of disease later in life, but more research is needed to confirm this. Soy formula is the best feeding choice for vegan families and babies with specific medical conditions.

Are soy isoflavones harmful to babies?

Soy formulas are naturally rich in isoflavones –– a plant compound with a structure similar to that of the hormone estrogen. Estrogen is, in large part, responsible for female sexual development (11).

Babies fed soy formula typically receive more soy isoflavones than babies who are breastfed or given cow’s milk formula. They also tend to consume more soy isoflavones than adults who enjoy soy as part of a diverse diet (3, 12).

Hence, some fear that soy formula may have estrogen-like effects at a time in development when estrogen levels are typically low. This fear is fuelled by older animal studies reporting various abnormalities in animals exposed to soy isoflavones (13, 14, 15, 16, 17).

However, it’s important to note that estrogen is much more potent than soy isoflavones, and that animals metabolize soy isoflavones differently than humans (3, 18, 19).

This could explain why human studies haven’t typically observed any significant long-term effects in soy formula-fed babies, including little to no difference in sexual development or brain, thyroid, and immune function (3, 20, 21, 22).

Soy isoflavones are often believed to negatively affect a baby’s sexual, immune, or brain development. However, human studies have found little to no differences in development between babies fed soy- or cow’s-milk-based formula.

Other potential concerns

The use of soy formula may raise a few additional concerns.

Higher aluminum and phytate levels

Soy-based formulas tend to contain higher levels of aluminum than breastmilk and cow’s milk formulas. High aluminum levels may negatively affect a baby’s brain and bone mass development (11).

Preterm babies, as well as babies with birth weights below 4 pounds (1.8 kg) or reduced renal function, appear to be most at risk. On the other hand, healthy babies born to term do not appear to be at risk (1).

Soy is also naturally rich in phytates, a compound that can reduce the body’s ability to absorb the nutrients found in foods. In theory, this may cause babies fed soy formula to receive fewer nutrients, although no studies currently confirm this (11).

May cause slightly longer, heavier, or more painful periods

A few studies suggest that girls fed soy formula as babies may experience longer, heavier, or more painful periods. One study also links soy formula use to a higher risk of endometriosis (23, 24, 25, 20).

However, these effects appear to be minor. For instance, one study found the onset of menstruation to be an average of 5 months earlier, and that longer periods lasted an average of 9 hours longer (20).

One recent study notes that babies fed soy formula from birth to 9 months appear to experience differences in gene activation and changes in their vaginal cells, compared with babies fed cow’s milk formula (26).

Still, more research is needed to determine whether these differences result in any significant long-term health implications.

Soy formula is linked to a higher risk of endometriosis and slightly longer, heavier, or more painful periods, although differences appear minor. Moreover, its higher aluminum levels may pose a risk to certain babies.

Who should choose soy formula?

Soy formula has been used to safely feed healthy babies for more than 100 years with few reports of long-term health problems. Thus, it can be considered an appropriate feeding choice for most babies (1, 3).

However, health organizations don’t recommend its widespread use, as it’s considered to offer little nutritional advantage over cow’s milk formula.

Therefore, soy formula use is typically only recommended for vegan families or those with full-term babies with galactosemia or hereditary lactase deficiency (1, 2).

That said, vegan families and parents of such children should consult a healthcare professional to determine whether a soy-based formula is the best option.

Soy formula may be an appropriate choice for some healthy infants. However, health organizations only specifically recommend its use for vegan families or those with full-term babies with galactosemia or hereditary lactase deficiency.

When to avoid soy formula

Soy formula isn’t a good choice for all babies.

Although considered safe for healthy, full-term infants, the higher aluminum content of soy formula may cause weaker bones in babies born pre-term, with birth weights below 4 pounds (1.8 kg), or with reduced renal function (1, 2).

Moreover, soy formula may not be a good choice for babies with an intolerance or allergy to cow’s milk protein, as up to half of these children may develop an intolerance to soy protein as well when given soy-based formulas. Thus, hydrolyzed formulas may be a better option (27).

Health authorities specifically highlight that although soy formula may be used to help babies grow and develop optimally, it generally doesn’t confer any advantages over a cow’s-milk-based formula.

This is why they typically recommend that healthy babies from non-vegan families and babies who do not have galactosemia or a hereditary lactase deficiency choose cow’s milk formula (1, 2).

Soy formulas are likely not appropriate for pre-term babies born, nor those born with poor renal function or a low birth weight. They may also not be the best choice for infants with cow’s milk allergy or intolerance.

The bottom line

Soy formula is likely safe for most healthy babies. It’s just as nutritious as other types of formula and likely the most beneficial choice for vegan families and babies with galactosemia or hereditary lactase deficiency.

Against popular belief, the evidence doesn’t support the claim that soy formula prevents colic or allergies or helps protect from disease later in life.

Moreover, soy formula is not an appropriate choice for babies born prematurely, nor those with low birth weights, poor renal function, or a cow’s milk allergy.

When in doubt, make sure to consult a qualified healthcare provider to determine which baby formula is most appropriate for your baby.