Despite the general thinking that soy is considered to be healthy, much controversy surrounds it’s use.  This includes the use of soy formula for infants who are fed virtually 100% formula, vs. toddlers or adults who consume a variety of foods and less soy as a percentage of their diets.  The safety of soy formula has been debated since it is made with a class of compounds called isoflavones.   These  isoflavones are referred to as phytoestrogens since they are found in plants (phyto) and since they act like the hormone estrogen in the body. 

                According to the AAP concerns raised in relation to phytoestrogens/isoflavones include their potential negative effects on sexual development and reproduction, neurobehavioral development, immune function, and thyroid function.  They go on to comment that although studied by numerous investigators in various species, there is no conclusive evidence from animal, adult human, or infant populations that dietary soy isoflavones may adversely effect human development, reproductive, or endocrine function. 

                Since the clinical report from the AAC in came out in 2008, a study done published in Biology of Reproduction (2010) reported  that newborn mice fed genistein-enriched soy formula during the first five days of life developed abnormalities of the ovary, uterus and thymus gland that were estrogen related and persisted into adulthood.  As adults, the mice had fewer reproductive cycles in a month than the untreated mice.  Again, this raises concerns for human infants fed soy-based formula during their early months but further research is still needed. 

                According to the AAP recommendations, in term infants, there are few indications for the use  of soy protein-based formula in place of cow milk-based formula.  These indications include (a) for infants with galactosemia and a condition called hereditary lactase deficiency (rare) and (b) in situations in which a vegetarian diet is preferred.  For infants with documented cow milk protein allergy, extensively hydrolyzed protein formula should be considered, versus soy formula, since 10%-14%  of these infants will also have a soy protein allergy.  They go on to recommend that soy protein-based formulas are not designed for or recommended for preterm infants, and that the routine use of isolated soy protein-based formula has no proven value in the prevention or management of infantile colic or fussiness.  The AAP promotes the use of human milk as the ideal source of infant nutrition.

Merritt, RJ., Jenks, BH.  Safety of soy-based infant formulas containing is flavones: the clinical evidence. J Nutr.  2004; 134 (5): 1220s-1224S.

Bhatia, J., Greer,F., and the Committee on Nutrition.  Use of Soy Protein-Based Formulas in Infant Feeding.  American Academy of Pediatrics, 2008.

Cimafrance, MA., J. Davila, GC Eckman, RN Andrews, SL Neese, J Peretz, KA Woodling, WG Helferich, J Sarkar, JA Flaws, SL Schantz, DR Doerge and PS Cooke, 2010.  Acute and chronic effets and oral genistein administration in neonatal mice.  Biology of Reproduction http://dx.doi.org/10.1095/biolreprod.109.080549.