Nutrition Bytes

Making up about 25% of the current infant-formula market in the U.S., soy-based infant formulas are lifesaving alternatives for infants who cannot rely on traditional sources of milk for complete nutrition. While many studies have supported the effectiveness of soy-formula consumption for normal growth and development, the controversy over the potentially harmful effects of early exposure to isoflavones (phytoestrogens found in soy formulas) remains to be resolved. The plasma concentration of isoflavones in soy-fed infants is so high that it is more than 13,000 times higher than that of estradiol found in early life (9). Since the exposure to high levels of estrogen during critical periods of development can exert detrimental consequences on reproduction, the high plasma level of isoflavones in soy-fed infants may cause similar physiological effects via their estrogen-like behaviors. One recent epidemiological study on humans has found little association between consumption of soy formulas during infancy and reproductive health (7). However, human data on this subject is scarce and animal studies (2,3,22,24) have yielded conflicting and complicated results. Thus, more research is needed before further claims can be made about soy formulas and their potential damaging effects on reproductive health.