Isoflavones
Related Terms
Coumestrol, daidzein, diet, edamame, frijol de soya, genistein, greater bean, haba soya, hydrolyzed soy protein, isoflavone, isoflavonoid, legume, natto, phytoestrogen, plant estrogen, shoyu, soja, sojabohne, soybean, soy fiber, soy food, soy product, soy protein soya, soya protein, Ta-tou(Chinese), texturized vegetable protein, tofu.
Background
The soy free diet is a way of eating that does not include soy or soy derivatives, such as tofu, tempeh, and miso. Usually, an individual will adopt a soy free diet to test for, or after discovering that they have, a soy allergy. Soy contains estrogen-like isoflavones, called phytoestrogens. The exact mechanism of these constituents is not clear. Soy may be beneficial in individuals with low estrogen levels, particularly post-menopausal women.
Soy has been a dietary staple to many Eastern cultures for thousands of years. Recently adopted into Western culture, soy offers many documented benefits including cholesterol reduction, improving thyroid function and weight control.
However, the World Health Organization includes soy in a list of the eight most significant food allergens. The incidence of allergy to soy is estimated to be 6%, but this is thought to be an underestimate due to difficulty in recognizing the symptoms of allergy. Soy allergy typically manifests in asthma-like breathing problems and skin rashes. In older adults, soy intolerant symptoms may include bloating, nausea, constipation, migraine headache, acne or eczema-like skin conditions, fatigue, and weakness.
At least 16 potential soy protein allergens have been identified, but the clinical relevance is unknown. Those most commonly affected are infants and young children with serious allergies to peanuts. Soymilk is often used as an alternative to cow's milk in lactose intolerant or allergic infants, however some potential exists for allergic cross reactivity.
Little research has been conducted to identify and evaluate the benefits, if any, of a soy free diet. Because of the low allergenic potential of soy, many people may be suffering from soy intolerance but cannot attribute their symptoms to any allergen or disease. People with atopic conditions, hormone dependant conditions such as some types of cancer and endometriosis, and those with food allergies or intolerances to soy products may benefit from implementing a soy free diet.
Theory / Evidence
Allergy is one reason why an individual may opt for a soy free diet. Food allergies involve the body's immune system. The offending substance (in this case, soy) is known as the allergen. Although recent investigation into allergies have shown that they create a complex cascade of events in the body, the basic process of a body's reaction to an allergen is the same as with other substances. When the allergen is ingested, the body's immune system reacts to what it perceives to be a foreign invader. The body releases an antibody known as immunoglobulin E (IgE), which interacts with the allergen. Specialized tissue and blood cells connected to the IgE antibody release a substance called histamine. It is histamine that is responsible for the uncomfortable, and sometimes life threatening symptoms which occur when an allergen is ingested.
Reactions to allergens occur throughout the body as the immune system tries to contain and eliminate the perceived invader. The most common reactions include the mouth, digestive tract, skin, and airways. The lips and mouth may swell. Stomach cramps, vomiting, and diarrhea may result. Hives, rashes, or eczema may appear on the skin. Wheezing or breathing problems sometimes develop.
Skin allergy testing (also called "scratch tests") are not always a reliable way to test for food allergies. Some individuals who are reactive to ingested food may not show a reaction on a scratch test. Scratch tests offer only a localized response to an allergen, whereas ingested food may have a more systemic effect. This is because the body changes food as it is digested. The body also is exposed to a significantly higher amount of the allergen during ingestion. The exclusion of soy products from the diet and lifestyle, therefore, may offer more comprehensive data on a possible allergy.
There are several theoretical risks associated with soy intake, which soy free dieters may be able to avoid. The phytoestrogens present in soy bind to estrogen receptors and exert both estrogenic and antiestrogenic effects. Phytoestrogens inhibit thyroid peroxidase, the enzyme responsible for converting T3 to T4. The exact clinical consequences of this are unknown, but several reports attribute thyroid cancer and goiter development to soy intake.
An area of concern has been whether phytoestrogens carry the same risks as prescription drug hormone replacement therapy (HRT), which contains estrogens, such as increased risk of hormone-sensitive cancers (breast, ovarian, uterine) or blood clots. This is an important area of concern for patients, as some women may consider soy as an alternative to HRT in order to avoid these risks. Early studies report that soy isoflavones do not cause the same thickening of the uterus lining (endometrium) as estrogen, and therefore may not carry the same risks as HRT. In addition, some scientists theorize that isoflavones may actually reduce the risk of cancer by blocking estrogen effects in the body, based on laboratory studies showing isoflavones to partially block (non-competitively inhibit) estrogen receptors. Additional research is needed in this area before a clear risk-assessment can be conducted.
Little research has been conducted to identify and evaluate the benefits, if any, of a soy-free diet. Because of soy's low allergenic potential, allergic symptoms may not appear every time soy is consumed or to the extent usually expected with food allergies. Instead, periodically the individual may complain of general malaise, bloating, or headaches.
Author information
This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
Bibliography
American Academy of Allergy Asthma & Immunology. 19 June 2006.
Cordle CT. Soy protein allergy: incidence and relative severity. J Nutr. 2004 May;134(5):1213S-1219S.
Food Allergy and Anaphylaxis Network. 19 June 2006.
Foodsafety.gov: Gateway to Government Food Safety Information. 19 June 2006.
National Food Service Management Institute. 19 June 2006.
International Food Information Council. 19 June 2006.
Wood CE. Dietary soy isoflavones inhibit estrogen effects in the post-menopausal breast. Cancer Res. 2006-Jan 15;66 (2):1241-9.
World Health Organization. 20 June 2006.
Diet outline
In the soy free diet, individuals do not consume any soy products. Individuals who adhere to a soy free diet should read food labels and become familiar with the many words for soy that may appear on food labels. Some example of terms for soy and common soy foods include doenjang, douche, edamame, G. max, ganjang, glycine max, miso, natto, shoyu (Japanese), soy sauce, soya (British English), soya bean (British English), tamari, tempeh, tofu. tofu, Worcestershire sauce.
Adherents may have to cook for themselves. Restaurants may use soy-based products in cooking or preparing food; at social gatherings, adherents may want to examine ingredient packages, or bring a food product that they know is soy free.
Identifying and avoiding ingredients that contain soy may appear challenging. A qualified healthcare professional and nutritionist should be consulted before making decisions about diets and/or health conditions.