With the media touting the health benefits of soy in recent years, many people have made a conscious effort to add more soy to their diets. But soy is controversial and its benefits are in dispute. According to Sally Fallon and Mary Enig, PhD., government researchers at the National Center for Toxicological Research initially wanted soy products to carry a warning label about the negative health effects. The majority of soy is also genetically modified, and it is unknown how these changes may affect the safety of soy.
Hypothyroidism
According to Mary Shomon, author of "Living Well with Hypothyroidism," excessive soy consumption can cause goiter. A diet high in soy can also suppress thyroid function, and cause or worsen hypothyroidism. Hypothyroidism causes symptoms such as weight gain, depression, muscle aches, weakness and fatigue. Soy also contains goitrogens, which depress thyroid function, according to Sally Fallon and Mary Enig, PhD. Goitrogens are naturally occurring chemicals that interfere with the thyroid's ability to use iodine in manufacturing thyroid hormones. Many people can eat goitrogenic foods without harm, but they can be detrimental for people prone to hypothyroidism. Consuming large amounts of soy foods may also increase the risk.
Estrogenic Effects
Soy has phytoestrogenic effects, which are natural, weaker forms of plant-based estrogen. A study led by Retha Newbold and Barry Delclos of the National Center for Toxicological Research found that high amounts of genistein, the protein in soy, disrupted reproductive cycles in rats. The study found that high soy consumption led to early puberty, irregular hormone cycles and smaller litters. It is possible that humans are similarly affected by soy. The researchers were concerned that infants fed soy formula could be at extra risk because they have the highest soy consumption by body weight.
Trypsin and Fermentation
Soybeans are usually fermented before they are safe for consumption. Fallon and Enig reported that unfermented soy contains trypsin inhibitors. Trypsin is an enzyme that aids in protein digestion. Inhibiting trypsin is linked to problems with digestion, growth and the pancreas, including enlargement and possibly cancer. Fermenting soy eliminates some of these problems, but not all.
Mineral Absorption
The husks of seeds and legumes contain phytic acid, also called phytates. Phytic acid blocks the absorption of key minerals the body needs, including magnesium, copper, zinc and calcium. Soybeans have the highest levels of phytic acid of any crop, and consumption of high amounts of soy can lead to nutrient deficiencies. A deficiency of these nutrients may lead to slow growth in children and reproductive problems.
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