Babies who drink soy formula receive significant amounts of estrogen-like compounds (phytoestrogens) in the form of soy isoflavones. This happens at a developmental time when permanent effects are theoretically possible. Some have speculated that soy formula might be responsible for early puberty in girls or infertility in boys.
The August 15, 2001 issue of The Journal of the American Medical Association (JAMA) contains the results of a study of 811 adults, some of who drank soy formula as children and others who drank milk-based formulas. No statistically significant differences were observed between the groups in either women or men. They followed more than 30 different measures of general health or reproductive health.
Breast milk is clearly the ideal food for babies, but this study is quite reassuring that soy formulas are a safe alternative. This is good news for babies who do not tolerate cow’s milk formulas well.