by Heidi Green
June 13, 2012
Soy-based formula was developed as an alternative food source for infants who didn’t have access to human milk and couldn’t tolerate cow’s milk protein. Soy-based formula was first released in 1929, but it wasn’t until federal regulations were introduced in 1971 that it gained acceptance. Soy formulas currently represent about 40 percent of U.S. formula sales.
Soy’s popularity is largely tied to the growing awareness of food allergies (particularly dairy) and lactose intolerance. Some parents who choose to formula-feed want to avoid giving their babies cow’s milk-based formula—hoping this will reduce their child’s risk of developing allergies. However, 35–50 percent of babies who are allergic to cow’s milk protein will also be allergic to soy protein. For these babies, breast milk is the best choice; but if that is not possible, parents should talk with their child’s health care provider about feeding options. Previously, the American Academy of Pediatrics (AAP) recommended a specialized infant formula made with hydrolyzed (partially digested) cow’s milk proteins. Now, the Food and Drug Administration (FDA) warns against the use of hydrolyzed formulas. (Read on for more details.)
Some parents select soy-based formula because they believe manufacturer’s claims (see here and here) that it is gentler on babies’ stomachs than milk-based formula. These claims are unsubstantiated by medical studies.
In spite of the AAP’s recommendation that soy formula be used only in special circumstances, a new study seeks to put soy-based formula on equal standing with cow’s milk-based formula. The study reaffirms that “breast is best.” But it also suggests that when it comes to babies’ cognitive and motor skills development, it may not matter which infant formula parents choose. This assurance should be taken with caution.
Researchers from the University of Arkansas sought to characterize the development of infants fed breast milk, cow’s milk-based formula, or soy protein-based formula from birth to 12 months.
Dr. Aline Andres and colleagues recruited 391 infants who were between 1–2 months old and were born following uncomplicated pregnancies to non-smoking mothers who didn’t use alcohol during pregnancy or soy/estrogenic compounds during pregnancy or lactation. They excluded those babies who were switched from milk-based to soy-based formula, or soy-based to milk-based formula, anytime during the study period, as well as those who received complementary foods before 4 months of age, and those with a low body weight at 3 months of age of less than 5 kg.
All formula-fed babies received either a milk-based formula (Similac Advance or Enfamil Lipil) or a soy-based formula (Similac Soy Isomil or Enfamil Prosobee), as chosen by their parents, until 12 months of age. Some of the “formula-fed” babies were initially breastfed; most infants were switched to formula at around 3 weeks of age, although roughly 10 percent of infants in each formula group breastfed until 6–8 weeks of age.
Breastfeeding parents were encouraged to continue giving their babies breast milk until 12 months of age, but nearly half (47 percent) chose to supplement with formula or switch to milk-based formula during the study period. (Keep reading for more about why switching matters.)
The researchers visited study participants at 3, 6, 9, and 12 months of age. They assessed babies for food intake, body weight and length, cognitive and motor development, and language skills. Information about mothers’ intelligence and socioeconomic status was also collected.
Dr. Andres and colleagues found no significant differences between infants fed milk-based formula and those fed soy-based formula for any measured indicator. Their results were within normal range for study participants, regardless of feeding type. However, the researchers did notice what they call “a slight advantage” for breastfed infants with regard to cognitive factors.
Several factors make this study difficult to interpret:
The AAP continues to recommend that infants be fed breast milk exclusively until 6 months of age, and alongside complementary foods, until at least 1 year of age. The World Health Organization (WHO) recommends that infants be breastfed exclusively for the first six months, at which point complementary foods may be introduced and breastfeeding continued until at least 2 years of age.
If you choose to formula-feed—exclusively or in conjunction with breastfeeding—be sure to choose your baby’s formula carefully. Unless your child’s pediatrician specifically recommends soy formula, you may want to consider a cow’s milk-based formula. For more information, see our guidance about iron-fortified formula as well as the AAP’s “Choosing a Formula” recommendations.
Editor’s Note—July 17, 2012
According to the FDA, “Partially hydrolyzed formulas should not be fed to infants who are allergic to milk or to infants with existing milk allergy symptoms.” (Emphasis the FDA’s.)
The agency recently completed its review of infant formula manufacturers’ claim that 100 percent whey-protein partially hydrolyzed formula reduces the risk of atopic dermatitis, and the results of the review were published in the journal Pediatrics.
The FDA rejected the manufacturers’ claim, finding that “there is little to very little evidence, respectively, to support a qualified health claim concerning the relationship between intake of [such formula] and a reduced risk of atopic dermatitis in partially breastfed and exclusively formula-fed infants throughout the first year after birth and up to 3 years of age.”
The FDA also ruled that infant formula manufacturers must include a warning statement that partially hydrolyzed formulas are not hypoallergenic and should not be fed to infants who are allergic to milk or to infants with existing milk allergy symptoms.
Parents of infants with a suspected milk allergy are encouraged to make decisions about their babies’ care and feeding “under a doctor’s supervision.”
The text of the FDA’s ruling is available on the agency’s website.
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