Take caution when using baby soy formula, a baby fed entirely with a diet based on soy products may develop a serious thyroid disorder.
Health problems may occur from using baby soy formula as the your baby's main nutrition.
Considering all of soy's health benefits, it is tempting for new and expectant mothers to see soy-based infant formula as a "miracle food" and to stock their pantries sky-high with the stuff. Well, hold on there, mama: That most vulnerable member of the population, an infant unable to breastfeed, stands at great risk of developing a serious thyroid disorder due to a diet based entirely on soy formula.
That disorder is hypothyroidism, or an underactive thyroid, and it is a common cause of fatigue, depression, obesity, constipation, extreme sensitivity to cold and a number of other symptoms, most so common that the disorder can go undiagnosed for years. Since hormones from the thyroid gland regulate all other glands in the body (and thereby all human growth and development), altered thyroid hormone levels in infants may lead to disorders of the central nervous system and abnormal psycho-motor development, as well as slowed sexual development later in life.
Most soy foods, excluding soy oil and soy sauce, contain estrogenic compounds, known as isoflavones. These compounds are commonly thought to be protective against heart disease, stroke, diabetes and osteoporosis, while reducing the risk of breast, prostate and uterine cancers. You may find it ironic, then, that isoflavones can also be responsible for bringing on a hypothyroid condition.
Recent research by Japan's Ishizuki Thyroid Clinic and New Zealand's Ministry of Health (MOH) has helped determine the degree of danger soy's isoflavones pose. MOH research from 1998 shows that infants fed solely a soy-formula diet are exposed to 16 times more isofilavones than the amount necessary to cause goiter (enlargement of the thyroid due to poor functions in adults. The danger is especially great if soy formula is given to infants for longer than three months. Because this danger has long been known, many manufacturers add iodine, which is necessary for thyroid function, to their formulas. This does tend to prevent the onset of goiter, but in many cases does not prevent the underlying hypothyroid condition indicated by the goiter.
Because of their many documented benefits, isoflavone supplements have become a common part of adult preventative medicine regimens. But the Ishizuki study showed that isoflavone intake by healthy adults could also have a thyroid-suppressing effect. The study concluded that 33 mg of soy isoflavones per day was sufficient to cause goiter in adults. Yet some popular supplements provide from 40 to 120 mg of soy isoflavones daily.
Hypothyroidism can be detected by your doctor through blood tests and can be treated, though not reversed. If your child was raised on soy formula and exhibits developmental problems, depression, obesity or especially low energy, it may be a good idea to have your pediatrician conduct the necessary checks. Through preventative measures, you could keep your child from suffering future effects of hypothyroidism.
For more information on the connection between soy foods and hypothyroidism, see Mary Shomon's book: Living Well With Hypothyroidism: What Your Doctor Doesn't Tell You That You Need to Know (Wholecare, 2000).
— Katie Mehrer