While most American women realize that breastfeeding is best for their baby, lifestyle choices and job realities can dictate the use of formula instead. Soy formula, used for centuries in Asia, but only since 1909 in the west, has become enormously popular, capturing 25 percent of the formula market. Unfortunately, it's not that simple. Adults who regularly eat soy may enjoy lower cholesterol, stabilized hormone balance and less risk of developing breast or prostate cancer. However, what's good for adults isn't always good for babies.
Infants react differently than adults to the high levels of disease-fighting phytoestrogens in soy.
But with infants, less than five percent are available to bind to receptors. Studies by the Animal and Veterinary Sciences Group at Lincoln University in New Zealand suggest this may pose a risk to the sexual development of infants and children, although the research is inconclusive. In 1996, Dr. Kenneth Setchell of the Children's Hospital Medical Center in Cincinnati studied five leading brands of soy-based baby milk. He found the products contain the phytoestrogen level of several contraceptive pills every day, about six to 11 times the amount that alters the menstrual cycle. In a 1991 study by Japanese researchers at the Ishizuki Thyroid Clinic, half of 17 healthy adult participants developed goiters following three months of eating 30 grams of soybeans a day.