No long-term effects of soy infant formula seen. (Scientific update: a review of recent scientific papers related to vegetarianism).

Concerns have been raised about the effects of exposure to soy in infancy and young childhood since soy products contain naturally-occurring estrogens (isoflavones). A recent study examined adults who were fed soy formula as infants; the results may help provide some insights into the safety of soy products for young children. Nearly 250 adults (ages 20-34) who had received soy formula as infants were compared to more than 500 adults who had received formula based on cow's milk. Study subjects were questioned about their heights, weights, ages at puberty, menstrual histories, difficulties with conception, birth defects in their own infants, and hormonal disorders. There was little difference among the groups in most areas. Use of soy formula appeared to have no effect on fertility, miscarriage rate, birth defects in offspring, and maturation. Subjects were estimated to have an average intake of soy isoflavones of 4.2 to 9.4 milligrams per kilogram of body weight daily as infants. (This would be the equivalent of about 1.5 servings of soy for the average two-year-old or four servings of soy for the average four-year-old.) Certainly, there may be differences in the way that infants absorb and metabolize soy isoflavones, as compared to older children and adults. However, the results of this study do suggest that moderate intakes of soy are safe for infants and young children.

Strom BL, Schinnar R, Ziegler EE, et al. 2001. Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood. JAMA 286:807-814.