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Potential Health Risks of Soy

Like all foods, soy has beneficial effects for many people but, in certain situations and some people, soy can be harmful. Some individuals who start consuming soy products may experience stomach upset or digestive problems such as diarrhea, bloating or constipation. In most cases, this passes after some time as the body adjusts to a soy diet or a person reduces a high amount of soy in the diet. However, some people are allergic to soy and their bodies will never adjust to it.

Most experts agree that a moderate soy intake of up to 25g of soy protein a day is generally safe. However, opponents argue that this is too high because people in Asia (China, Japan) where soy has been part of a traditional diet for centuries only consume about 10g of soy products a day and most of it is fermented. Also, soy protein has never been granted GRAS (generally recognized as safe) status by the FDA. In fact, the long-term health impact of isolated substances from the soy protein or from consuming larger quantities of soy is still under investigation.

Recently, there has been some speculation about other health risks associated with soy products. Most of these concerns focus on specific components of soy such as antinutrients in unfermented soy products or isoflavones rather than on the whole food or the soy protein (for more information on the effects of antinutrients from a high soy diet please refer to this post).

Some of the most studied health problems associated with soy consumption include:

Endocrine function and cancer. This problem has to do with soy isoflavones. Isoflavones are phytoestrogens, a weak plant-based form of the hormone estrogen that can mimic the body’s own estrogen and even block its activity in the body. This effect may disrupt endocrine function and is most likely to occur in postmenopausal women. However, the data is mixed. While some studies suggest that high levels of soy isoflavones may lead to increased risk of cancer, others suggest that they may actually help prevent cancer.

Thyroid problems and goiter. Several studies have looked into the effects of goitrogens found in soy protein, concluding that these substances may disrupt the production of thyroid hormones. As a result, this could contribute to the formation of a goiter, an enlargement of the thyroid gland. However, there is no convincing evidence to date that moderate consumption of soy protein has an adverse effect on thyroid function in healthy individuals with adequate iodine status.

Weight gain. People who are watching their weight should keep in mind that soy foods do contain moderate amounts of fat. However, since most of that fat is unsaturated, it does not increase the levels of LDL cholesterol in the blood and thus does not contribute to clogged arteries and heart disease.

Soy infant formula. Many scientists question the use of soy infant formula and its allegedly positive effects on a child’s long-term health. Soy infant formula is a heavily processed product because soy milk does not exist in nature. It is used as an alternative to cow’s milk formula in children who need to avoid cow’s milk or lactose (milk sugar) for medical reasons. Feeding infants with soy formula milk dramatically (13-22,000 times) increases the levels of isoflavones (plant-derived substances that can mimic estrogen in the body) in their blood. Some studies suggest that infants fed with soy formula are more prone to developing peanut allergy and suffer sexual and reproductive problems later in life whereas those with inadequate iodine intake may also develop goiter. In addition, some children who use soy formula milk have been reported to experience diarrhea, vomiting, damage or bleeding of the intestinal wall and slow growth.

In summary, the following major concerns have been raised by scientists studying the health effects of soy:

  • Disruption of endocrine function due to high concentrations of isoflavones in soy may alter menstrual cycle and lead to infertility and breast cancer in women.
  • Thyroid problems (e.g., goiter) in individuals with insufficient iodine status due to high levels of goitrogens in soy.
  • Genetically modified soy may cause infertility and sexual dysfunction in future generations.
  • Poor absorption of certain minerals caused by phytates present in soy.
  • Digestive problems and poor absorption of protein due to the activity of protease inhibitors contained in soy.
  • Gastric distress and problems with absorption of vital nutrients due to damage of the intestinal wall caused by lectins and saponins found in soy.
  • Clotting of red blood cells caused by hemagglutinin in soy may result in poor oxygen delivery to the tissues.
  • Adverse effects on sexual development and reproductive health of babies fed with soy infant formula.
  • Genistein, one of the soy isoflavones, has been reported to impair immune function.
  • Consuming soy may cause deficiencies in vitamins B12 and D and calcium because soy foods increase the body’s requirement for these nutrients. This can result in increased risk of osteoporosis despite general belief that soy helps to keep it off.
  • Oxalate found in soy products can bind calcium and contribute to the formation of kidney stones. Oxalate levels are particularly high in foods made with textured soy protein.
  • Various phytochemicals in soy (especially isoflavones) may cause brain damage and speed up brain aging, thus contributing to Alzheimer’s, Parkinson’s and dementia later in life.
  • Like peanuts (which are botanically related to soybeans), soy is a common cause of food allergy.

Conclusion. It needs to be mentioned that the aforementioned risks are mainly associated with consuming non-fermented soy foods such as tofu or soy milk. Fermented soy products contain significantly lower amounts of toxins and antinutrients and, therefore, pose no health risk when consumed in reasonable amounts. In addition, processed soy foods are often contaminated with chemicals, such as hexane, aluminium or manganese, used in extraction and refining. High levels of these chemicals may also cause health problems in some people.

Where to Find More Information: Straight Talk about Soy from Harvard University