What Is Soy Baby Formula?

Mother bottle-feeding her infant daughter
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What Is Soy Formula?

Soy formula is a substitute for human milk and cow's milk-based formula that is manufactured from soy protein. Soy infant formula products are intended for babies under 12 months old. These products account for 12% of the formula market.

The use of soy-protein-based baby formula is popular with some parents because they believe that it can help relieve gas, fussiness, or colic. However, switching baby formulas doesn't usually relieve these symptoms. Experts say that parents shouldn't be quick to switch to soy formula over breast milk or cow's milk formula unless it is medically indicated.

Why It’s Used

In some cases, soy-based formula can be an optimal feeding choice for an infant. While soy formula has not been proven to help with things like fussiness or eczema, babies with certain health conditions may benefit from soy-based formula when breast milk is not available by circumstance or choice.

Soy formula may be a good choice for the following:

  • Galactosemia, a condition in which an infant is unable to break down the sugar galactose
  • Primary lactase deficiency, a rare hereditary condition in which a baby is born without the enzyme lactase, which is required to digest the sugar lactose
  • Secondary lactase deficiency, a temporary lactose intolerance, usually caused by an infection that affects the gastrointestinal tract
  • Families who are vegetarian or vegan

The vitamin D in soy formula is generally sourced from lanolin, so soy formulas aren’t purely vegan, but they are likely as close as you can get to a vegan or plant-based infant formula.

Types of Soy Formula

If your pediatrician thinks that soy formula is necessary for your baby, be assured that these products are just as good as other formulas and are readily available wherever baby formula is sold. All brands of formula are regulated by the Food and Drug Administration (FDA) and must meet strict nutrition and safety standards.

Soy baby formula options include:

  • Enfamil ProSobee
  • Similac Soy Isomil
  • Gerber Good Start Soy
  • Parent's Choice Soy (Walmart's store brand)
  • Earth's Best Organic Soy Infant Formula

Tips for Switching

If you are thinking about making a switch to soy formula, be sure to discuss your plan with your child’s pediatrician first. They will be able to advise you about your specific circumstances. 

If your doctor agrees with the need to switch your baby to soy formula, here are some things to keep in mind while you make the transition:

  • Ask your baby's doctor whether you should make the transition all at once or if you should gradually introduce the new formula.
  • Read the formula label: Be sure to measure and mix the formula accurately.
  • Check to be sure that the new formula does not contain ingredients that your baby is sensitive or allergic to.
  • Check the container for expiration dates.

While making the transition, watch your child closely for reactions to the new formula. Talk to your baby’s pediatrician if you notice digestive problems, rashes, or blood in your baby's stools or vomit as these symptoms may indicate an allergy.

Is Soy Formula Safe?

Soy milk formulas are approved by the FDA and contain the required nutrition for infants. There are, however, some specific concerns to keep in mind about soy formula.

Phytoestrogens

Phytoestrogens, especially the isoflavones found in soy, may have estrogen-like activity. Some experts have raised concerns about the potential for phytoestrogens to affect things like sexual development and immune and thyroid function. 

Some research has found a link between heavy menstrual bleeding and soy formula feeding in infancy. Other research suggests that menstruating people who were fed soy formula as infants may be more likely to experience more painful periods. Another study found altered vaginal DNA cells in those who were fed soy formula in infancy.

At the same time, isoflavones may offer certain protections against heart disease and certain cancers. Research is ongoing as to the health implications of phytoestrogens on humans, especially infants.

Aluminum

Soy-protein formula contains a relatively high level of aluminum compared to breast milk and cow's milk-based formula. This exposure is not thought to be a problem for full-term infants but may lead to reduced bone mineralization in preterm babies, especially those with renal function or renal failure. Healthy, full-term infants are not at substantial risk of aluminum exposure from soy formula.

Soy Formula vs. Soy Milk

Soy formula and soy milk are entirely different products. Soy formula is made of soy protein and other ingredients specifically designed to meet an infant’s nutritional needs. Soy milk, on the other hand, is made of soybeans and filtered water. It does not contain the necessary ingredients to meet an infant’s nutritional needs and should never be used as a substitute for breast milk or formula for a baby younger than a year old.

For toddlers, soy milk is sometimes used as an alternate milk source. Whole milk is recommended for toddlers between 12 and 23 months of age because it contains the fat toddlers require for growth. It’s important to remember that soy milk does not have the equivalent amount of fat per serving as whole cow’s milk (4 grams of fat to cow’s milk’s 8 grams). If you do give your toddler a reduced-fat milk, such as soy milk, be sure to make up for that missed fat in other parts of your child's diet.

When to Avoid Soy Formula

Soy formula is not recommended unless a baby has a rare health condition or a family is strictly vegetarian or vegan. In addition, soy formula is not recommended for some specific situations.

Avoid soy baby formula for:

  • Colic or fussiness, since the switch will likely not be helpful
  • A cow's milk protein allergy, since many infants who have a cow's milk allergy are also allergic to soy proteins and should drink an extensively hydrolyzed protein formula instead
  • A high risk for food allergies, since soy is among the most common allergens
  • Premature babies, since soy formula can lead to decreased bone mineralization, even when babies are given supplemental calcium

Unless there is a good reason to start your baby on soy formula, if you stop breastfeeding before your baby is 12 months old or need to supplement, it is best to start with a cow's milk-based formula rather than soy formula.

A Word From Verywell

Unless your baby has a rare health condition or your family's diet is strictly plant-based, soy formula is generally not recommended. Infants with cow’s milk sensitivities or allergies may also have the same reactions to soy, in which case, hypoallergenic formulas are often a better alternative. If you are considering switching formulas, be sure to consult your baby’s pediatrician for guidance.

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Article Sources
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  2. Bhatia J, Greer F. Use of soy protein-based formulas in infant feeding. Pediatrics. 2008;121(5):1062-1068. doi:10.1542/peds.2008-0564

  3. American College of Gastroenterology. Lactose intolerance in children.

  4. U.S. Food and Drug Administration. Infant formula guidance documents and regulatory information. Updated May 8, 2019.

  5. Upson K, Harmon Q, Laughlin-Tommaso S, Umbach D, Baird D. Soy-based infant formula feeding and heavy menstrual bleeding among young african american women. Epidemiology. 2016;27(5):716-725. doi:10.1097/ede.0000000000000508

  6. Upson K, Adgent M, Wegienka G, Baird D. Soy-based infant formula feeding and menstrual pain in a cohort of women aged 23–35 years. Human Reproduction. 2018;34(1):148-154. doi:10.1093/humrep/dey303

  7. Harlid S, Adgent M, Jefferson W et al. Soy formula and epigenetic modifications: Analysis of vaginal epithelial cells from infant girls in the IFED study. Environ Health Perspect. 2017;125(3):447-452. doi:10.1289/ehp428

Additional Reading
  • American Academy of Pediatrics. Guide to Your Child's Nutrition.
  • American Academy of Pediatrics Clinical Report. Use of Soy Protein-Based Formulas in Infant Feeding. PEDIATRICS Vol. 121 No. 5 May 2008, pp. 1062-1068.