I would not not not feed a baby soy formula (unless it is truly medically necessary. For instance because the baby has a congenital lactose intolerance—which is VERY, VERY rare and diagnosed in the testing they do right after birth). There is mounting research that soy formula can cause harm to a child’s developing endocrine system, could be linked to ADHD and early onset of menses in girls and early formation of breast tissue, and that soy formula might have dangerous levels of aluminum and manganese.
In the U.K., Isreal, France, and New Zealand they have severely restricted or banned the use of soy formula for babies because of the mounting research on the adverse health effects. In the U.S. and Canada, the outcry has been much weaker and slower in response, but nevertheless, the American Academy of Pediatrics has updated their stance on the use of soy formula to be far more restrictive and cautionary than before. First, they remind readers that: “The AAP is committed to the use of human milk as the ideal source of nutrition for infant feeding.” Then, they go on to say that despite there being very few cases when using soy milk is really indicated medically it still makes up more than 20% of formula sales in the U.S. (REMEMBER: your baby isn’t lactose intolerant and you just don’t know it–remember breastmilk is very high in lactose so a truly lactose-intolerant baby would have never survived its first few weeks of life until very recently). The AAP goes on to acknowledge the: “potential harmful effects of soy protein-based formulas and the phytoestrogens they contain.”
They conclude by saying that you should NOT feed your baby soy formula unless it is truly necessary (either medically in the case of a diagnosis of galactosemia or hereditary lactase deficiency” or if parents insist on soy due to religious or cultural beliefs against all animal products.