Soy-based infant formula

Does my baby need soy-based infant formula?

Soy-based infant formula is made from soybeans instead of cow’s milk and contains different proteins and sugars. It is only recommended for babies with one of two conditions: galactosemia or congenital lactase deficiency, disorders that affect how the body uses sugars found in milk. There are several concerns about soy-based infant formula: it has high levels of aluminum and estrogen-type hormones; it can increase the risk of soft bones in small, premature babies; and babies with low thyroid levels may need special monitoring when using it. Some parents choose soy-based infant formula in order to avoid dairy products for personal, cultural, or religious reasons. Babies with milk allergies may tolerate it, but it is usually not recommended as a first treatment because they may also be allergic to soy products.

A) Soy-based infant formula

Soy-based infant formula (formula) is based on soybeans instead of cow’s milk. It is supplemented with amino acids, which babies need to make protein. Instead of the milk sugar lactose, it contains sugars such as:

  • Corn maltodextrin
  • Corn syrup
  • Corn syrup solids
  • Sucrose

B) Concerns about soy-based infant formula

There are a number of concerns about soy-based formula.

1) Estrogenic effects

Soy-based formula has high levels of estrogen-type hormones (Bhatia 2008; Harlid 2017; Ho 2017; O’Connor 2009). Compared to breast-fed babies or those receiving cow's milk-based formula, there have been reports of babies using soy-based formula having higher levels of these hormones (Patisaul 2010).  

Studies have related soy-based formula to:

  • Increasing the amount of breast tissue in the second year of life (Zung 2008).
  • Causing changes in the vagina and uterus of baby girls consistent with excess estrogen exposure (Adgent 2018; Bernbaum 2008).
  • Causing longer and more painful periods (Strom 2001; Upson 2018).
  • Increasing the risk of endometriosis, a condition in which tissue similar to the lining of the uterus grows outside of it (Upson 2015).
  • Early puberty in girls (Felício 2021).

Currently, most researchers report there is no conclusive evidence that soy-based formula affects long-term development or hormone function of babies (Oliviera 2021; Testa 2018).

2) Aluminum

While all formulas contain aluminum, soy-based formula has particularly high levels (Bhatia 2008; Chuchu 2013; Kazi 2009). There have been concerns that this can affect the brain, nervous system, and bones of babies.

3) Soft bones

Soy-based formula is not recommended for premature babies, as it can increase the risk of soft bones (osteopenia) (O’Connor 2009).

4) Thyroid problems

Some babies are born with low thyroid hormone levels and are treated with replacement hormones. Soy formula can prevent these from being absorbed.

Babies in this situation may need special monitoring if given soy-based formula (Leung et al. 2009; Testa et al. 2018).

C) Using soy-based infant formula

Soy-based formula is only recommended for babies with galactosemia, a disorder that affects how the body uses the milk sugar component, galactose and congenital lactase deficiency, an inability to digest lactose (Leung 2009). Both are relatively rare.

Some babies who are allergic to milk protein can tolerate soy-based formula but it is not usually recommended as the first treatment.

Some parents choose soy-based formula in order to avoid dairy products for personal, cultural, or religious reasons.

Rates of soy-based formula use varies between countries. One review (Rosen 2016) showed that in the United States 16% of children received soy-based formula

D) When soy-based infant formula is not recommended

Soy-based formula is usually not recommended as a first treatment for babies with milk allergies because they may also be allergic to soy products (Leung 2009). Of babies with cow’s milk protein allergy, 10% to 14% will also react to soy protein (Bhatia 2008; ESPGHAN 2006). Rather such babies are usually given extensively hydrolyzed formula.

 Soy-based formula is not recommended for small, premature babies.


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