In a new study, researchers from Children’s Hospital of Philadelphia find that babies fed by soy-based formula had differences in the reproductive-system compared with babies fed with cow-milk formula or breastmilk.
Although the differences were subtle and not a cause for alarm, it needs further research of the long-term effects.
Soy formula contains high concentrations of plant-based estrogen-like compounds.
Because this formula is the sole food source for many babies in the first six months of life, it’s important to understand the effects of exposure to such compounds during a critical period in development.
Some mothers who don’t breastfeed have long used soy formula as an alternative to cow-milk formula.
They have concerns about milk allergies, lactose intolerance, or other feeding difficulties.
However, soy protein contains high amounts of genistein, an estrogen-like compound.
Like other estrogen-mimicking chemicals found in the environment, genistein can alter the body’s endocrine system and may interfere with normal hormonal development.
In previous studies, genistein causes abnormal reproductive development and function in rodents. But little is known about its effects on infants.
In this study, the team compared infants fed with soy formula to those fed with cow-milk formula and breastfed infants.
A total of 283 pairs completed the study. Of those, 102 infants exclusively fed on soy formula, 111 on cow-milk formula, and 70 on breast milk.
They were born in eight Philadelphia-area hospitals between 2010 and 2013, and enrolled in the Infant Feeding and Early Development (IFED) Study.
All of the infants were evaluated at the hospital, and researchers repeatedly performed measurements up to age 28 weeks in the boys and age 36 weeks in the girls.
They found that compared to girls fed cow-milk formula, those fed soy formula had developmental trajectories consistent with responses to estrogen exposure.
In addition, the babies’ vaginal cell MI was higher and uterine volume decreased more slowly in soy-fed girls, both of which suggest estrogen-like responses.
The study team found similar patterns in differences between soy-fed girls and breastfed girls.
The researchers don’t conclude whether the effects we found have long-term consequences for health and development, but the question merits further study.
For mothers who prefer giving formula, the AAP does not recommend soy formula for preterm infants, but states that soy formula is indicated for infants with hereditary disorders that make them unable to digest milk.
It also recommends soy formula “in situations in which a vegetarian diet is preferred.”.
The study was funded and led by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health.
The first author is Margaret A. Adgent, MSPH, PhD, formerly of NIEHS, now at Vanderbilt University Medical Center.
Virginia A. Stallings, MD, director of the Nutrition Center at Children’s Hospital of Philadelphia, is a study senior author.
The study is published in the Journal of Clinical Endocrinology and Metabolism.
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Journal reference: Journal of Clinical Endocrinology and Metabolism.
