The American Academy of Pediatrics estimates that about 25 percent of infants in the U.S. receive soy formula in their diets. While many parents believe that soy formula is healthier than formulas with cow’s protein, pediatricians say that few babies actually have medical conditions, which warrant a need for soy formula. Before making the choice to start your baby on a soy formula, both you and your infant’s pediatrician should examine all the alternatives. Then carefully weigh the possible benefits of each against any potential adverse side effects on your baby’s health.
In recent years, consumer advocacy groups have voiced concerns that high levels of isoflavones, also known as photoestorgens, found in soy formulas may affect a child’s endocrine system. In particular, the isoflavones in soy are thought to act similarly to the female hormone estrogen. Following a study conducted at the University of Pennsylvania, which was later published in the Journal of the American Medical Association (JAMA), researchers concluded that there were no statistically significant differences in the reproductive health of subjects who were fed soy formula during infancy. Nonetheless, considering that the developmental stages during which infants are fed formula could make negative long-term effects possible, research in the area continues. Another study published by the National Academy of Sciences suggests that isoflavones in soy might suppress the immune system. Investigators point out that while the study shows no convincing evidence that soy formula is harmful to babies, mothers are encouraged to breast feed their infants or feed them milk-based formula unless there is a medically necessary reason why a baby needs soy formula.
While the AAP Committee on Nutrition cites lactose intolerance as being the primary reason why most parents switch their babies from milk-based to soy protein formulas, doctors say parents need to understand that allergies to soy formula are almost as common as allergies to cow’s milk. But because of concerns that infants absorb calcium and other essential nutrients less effectively from soy formulas than from milk-based formulas, a statement issued by the American Academy of Pediatrics recommends soy as nutrition only for those babies who have an allergy to the proteins in cow’s milk, or are lactose intolerant. There are also other alternatives such as lactose-free and hypoallergenic formulas now available if a baby is lactase deficient or at risk for food allergies. Despite fears that the high levels of phytic acid in soy could affect a baby’s growth and development by reducing the absorption of calcium, the National Institutes of Health (NIH) Office of Dietary Supplements points out that even though soybeans are high in phytic acid, the calcium in soy is still partially absorbed. Phytates in soy are blamed for blocking iron absorption, but the AAP argues that the amount of iron in breast milk is low as compared to that in iron-fortified formulas, yet infants absorb half of the iron in breast milk and only about 4 percent of that in formulas.
In studies conducted by the USDA Agricultural Research Services to investigate potential adverse effects of soy formulas, researchers found that soy proteins might affect the rate at which the body metabolizes medication. Animal studies show that substances in soy change certain enzymes in the liver, which are responsible for the break down and concentration of medications in the bloodstream. Increased levels of these enzymes in the body could affect absorption of the drug or increase the rate at which medications are metabolized. This would eliminate the drugs from the body faster, reducing levels of the drug in the bloodstream sooner, thereby decreasing its effectiveness for treating illness. Additional studies are currently underway to examine how this effect on infants who are fed soy formula compares with babies who are breastfed or receive milk-based formulas.