by Amy Spangler
February 04, 2010

The expression, “You are what you eat,” takes on new meaning, given the results of a recent study linking soy formula in babies with uterine fibroids in adults. Uterine fibroids are non-cancerous tumors of the uterus that commonly cause pelvic pain, vaginal bleeding, and fertility problems. Approximately one-fourth of women develop uterine fibroids which are the leading cause of hysterectomy (removal of the uterus).

Research
Twenty thousand white women between 35 and 59 years of age participated in the study. The women were selected from a larger group of 50,000 white women who are part of the Sister Study, a long-term review of women ages 35–74 who have never had breast cancer themselves but whose biological sister was diagnosed with the disease.

Women were asked whether they had ever been diagnosed with uterine fibroids and their age at diagnosis. They were also asked about a variety or early childhood exposures including whether they had been fed soy formula. Women were asked to choose from the following responses: definitely, probably, probably not, or definitely not fed soy formula.

Results
Women who were fed soy formula as babies were 25 percent more likely to develop uterine fibroids compared to those who were breastfed or fed cow milk formula. The link between uterine fibroids and soy formula is thought to be a response to the isoflavones (naturally occurring estrogen-like substances) in soy, and in particular, the high exposure at an early age in women given soy formula during infancy.

Although the American Academy of Pediatrics (AAP) recommends that babies be exclusively breastfed for the first six months of life, eight out of ten U.S. babies are given some type of artificial milk by 3 months of age. Soy formulas account for nearly 25 percent of the infant formula market. In 2008, the AAP’s Committee on Nutrition released a revised policy statement on the use of soy formula in infant feeding:

• Indications for use are rare and include metabolic disease or vegetarianism.

• Infants with documented cow’s milk allergy should be fed hydrolyzed formula, because 10–14 percent of these infants will also be allergic to soy.

• Once infants with severe diarrhea are rehydrated, they should be maintained on human milk or diluted cow’s milk formula.

• Soy formula has no advantage over cow’s milk formula as a supplement for the breastfed infant.

• Soy formula should not be fed to preterm infants.

• Use of soy formula does not alleviate colic or fussiness.

• Use of soy formula does not prevent allergic disease in high risk babies.

Recommendations
Concerns over the long-term health effects of soy formula are justified given that infants fed soy formula receive high levels of estrogen-like compounds relative to their body size. Until more data is available, parents are advised to follow the AAP policy and give soy formula only when medically indicated. If a baby is unable to breastfeed and human milk is not available, cow’s milk formula should be used.