Infants fed soy formula are the segment of the U. S. population that consumes the most soy. Before birth and after weaning, most Americans are not exposed to appreciable levels of soyfoods other than foods that have small amounts of processed soy components. The opposite scenario occurs in Asia, because Asians are more likely to consume relatively high levels of soyfoods throughout life, except between birth and weaning, when breastfeeding or milk-based formula are common. Soy formula is made with soy protein isolate containing isoflavones (SPI+) and supports normal growth and development in term infants. Recent data suggest that there are no long-term adverse effects of early exposure to soy formula through young adulthood. It is as yet unknown whether soy formula consumption by infants will result in health problems or benefits upon aging, but multigenerational animal studies with diets made with SPI+ have not revealed any problems. Soy isoflavones can function as estrogen agonists, antagonists or selective estrogen receptor modulators, depending on the conditions, and much research has focused on health effects of purified isoflavones. Results from several studies suggest that the effects of diets made with SPI+ differ significantly from those of diets to which purified soy isoflavones are added. Furthermore, it seems that soy protein processed to contain lower levels of isoflavones also provides significant health benefits. Further research is needed to confirm the results of the few studies that have been conducted and new studies are needed to investigate the more subtle effects that could occur during development or that could surface later in life.