Soy consumption in the United States has skyrocketed since the early 1990s, with soy food sales climbing from $300 million in 1992 to over $4 billion in 2008. Soy is a common ingredient found in many foods across the country, including meat products, milk, baked goods, breakfast cereals, vegetarian meat substitutes and even chocolate. Soy is recommended as part of the American diet by the U.S. Food and Drug Administration for its potential to decrease the risk of developing heart disease. Although touted for its health benefits, some studies suggest that soy may have a negative effect on health. Because the isoflavones in soy may interfere with hormones, most of the negative side effects that are reported are hormone related.
Female Fertility
The positive health benefits associated with eating soy come from the plant compounds that mimic estrogen. It is those estrogenic compounds, or isoflavones, that may alter female hormones if too much soy is consumed. This can result in decreased reproductive health, including loss of fertility, disrupted ovulation, irregular menstrual cycles and early puberty in girls.
Thyroid Problems
Soy is a phytoestrogen that mimics the function of hormones in the body. This can interfere with the thyroid gland, which produces and stores hormones that keep your body systems functioning properly. Thyroid hormones are responsible for regulating heart rate, keeping blood pressure balanced, converting food to energy at the appropriate metabolic rate and maintaining proper body temperature. According to Dr. Mike Fitzpatrick, an environmental scientist and phytoestrogen researcher who has conducted in-depth studies on soy, soy products can have a detrimental effect on both adults and infants because of their anti-thyroid capabilities.
Fetal Development
Because of the way soy products mimic estrogen and may possibly interfere with thyroid hormones, it is possible that pregnant women who eat large amounts of soy may be subjecting their fetus to hormonal interference. If hormones are altered during pregnancy, fetal development may be disrupted. There are limited human studies on the harmful effects of soy isoflavones, however, according to Retha Newbold, a developmental biologist at the National Institute of Environmental Health Sciences, there's strong evidence from animal studies that the isoflavone genistein alters reproduction and embryonic development.
Infant Formulas
Twenty-five percent of babies who are bottle-fed are given soy formula. Soy formula is commonly given to infants who are allergic to dairy milk. According to Dr. Sears, even though soy-based formulas may be less allergenic for some babies, between 30 and 50 percent of infants who are allergic to cow's milk are also allergic to soy. Because soy proteins do not contain all of the amino acids that a baby needs, they need to be added to the formula in large quantities. Dr. Sears states that feeding a young infant soy formula before the intestines have closed completely may predispose the infant to soy allergies later on. Soy formulas also contain approximately thirty-three percent more sodium than dairy formulas. Soy formulas do not contain lactose, the sugar found in human and cow milk that aids in calcium absorption and helps the intestines maintain adequate amounts of good bacteria.
According to Retha Newbold, giving an infant or child estrogen is never a good thing, but the amount of estrogenic compounds consumed by an infant ingesting soy formula is up to 11 times greater than the amount deemed necessary to alter adult hormone levels.
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