Scientists suggest that though the difference measured in the newborns were subtle, long time exposure to these estrogen-like compounds in soy-based formulas must be investigated.
‘Infants who consumed soy-based milk formula showed changes in their reproductive tissues’
According to Virginia A. Stallings, MD, director of the Nutrition Center at Children's Hospital of Philadelphia (CHOP), high concentrations of plant-based estrogen-like compounds are present in soy formula. He also indicated that long-term effects of these compounds should be studied as this formula is the main food source for many infants.
Another scientist Margaret A. Adgent, MSPH, PhD said that the modern soy formula is being used safely for a long time. However, small changes were seen in reproductive tissues but the long-term health effects associated with this are not known.
Effect of Soy-formula
Babies who were breastfed and consumed soy-formula for a long time instead of cow-milk formula faced few difficulties like milk allergies, lactose intolerance and other feeding difficulties. The soy-proteins contain high amounts of genistein, an estrogen-like compound.
Genistein can alter the body's endocrine system and eventually affect the normal hormonal development. Previous studies have shown that genistein caused abnormal reproductive development and functions in rodents, but its effect on infants was not known.
The current study highlights the postnatal development in estrogen-responsive tissues, along with specific hormone levels, according to infant feeding practices. The scientists compared infants who were fed with soy formula and those fed with cow-milk formula and breastfed infants.
About 410 infant-mother pairs enrolled in the investigation, out of which 283 of them completed the study. Among them 102 infants purely fed on soy formula, 111 on cow-milk formula, and 70 on breast milk. Stallings said that this was an observational study and not a randomized trial. The feeding preferences were decided by the mothers before they enrolled for the study.
More than half of the infants were girls and 70 percent were African-American born at eight Philadelphia-area hospitals between 2010 and 2013. These infants enrolled in the Infant Feeding and Early Development (IFED) Study.
All the babies were evaluated at CHOP, and researchers repeatedly performed the measurements up to 28 weeks of age in boys and 36 weeks of age in girls. The study team analyzed three sets of results: ultrasound measurements of uterine, ovarian and testicular volume, a maturational index (MI) based on epithelial cells from the children's urogenital tissue and hormone concentration through blood tests.
Stallings indicated that the main differences related to different feeding preferences were seen among girls. Girls who were fed with soy-based formula had higher vaginal cell MI and decreased uterine volume.
The study team found similar patterns in differences between soy-fed girls and breastfed girls. He also said that the long-term consequences of these effects were not known and the infants should be analyzed later during their childhood and adolescence period.
She added, "For new and expectant mothers deciding on how to feed their infants, as always, we strongly support breastfeeding, as recommended by the American Academy of Pediatrics." 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 properly digest milk, such as galactosemia and the rare condition hereditary lactase deficiency. It also recommends soy formula "in situations in which a vegetarian diet is preferred."
- EMargaret A Adgent, David M Umbach, Babette S Zemel, Andrea Kelly, Joan I Schall, Eileen G Ford, Kerry James, Kassa Darge, Julianne C Botelho, Hubert W Vesper, Donald Walt Chandler, Jon M Nakamoto, Walter J Rogan, Virginia A Stallings. A longitudinal study of estrogen-responsive tissues and hormone concentrations in infants fed soy formula. The Journal of Clinical Endocrinology & Metabolism(2018)