Tofu is a valuable source of protein for vegetarians, vegans and those who simply want to reduce their reliance on meat. It's made by processing soybeans into soy milk, then turning the milk into curds in much the same way cheese is made from cow's milk. Although tofu is a healthy food, it can cause allergic reactions in some people.
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Allergies and Allergens
An allergic reaction occurs when your body mistakes a normally innocuous substance as a threat to your health. Your immune system overreacts, triggering antibodies and histamines that cause a variety of reactions, ranging from a mild rash to life-threatening shock. Substances that trigger allergic reactions are called allergens. Some foods trigger unpleasant or uncomfortable reactions that don't involve your immune system. These are referred to as sensitivities by the medical profession, rather than allergies.
Soy and Other Primary Allergens
The Food and Drug Administration has identified eight especially common allergens, which collectively account for approximately 90 percent of all known food allergies. These eight are milk, eggs, fish, crustaceans such as lobster and shrimp, tree nuts, peanuts, wheat and soybeans. Soybeans and soybean-derived foods such as tofu and tempeh are daily staples for only a minority of Americans, but soy's widespread use in industrial food processing makes it a difficult allergen to avoid completely.
Tofu and Food Allergies
Tofu, made primarily of soy protein, is an unquestioned trigger for anyone with a soy allergy. Other ingredients will vary from brand to brand, but for the most part are unlikely to cause allergic reactions. The soy curd is coagulated commercially with calcium sulfate or other salts, which are not allergens but might cause a reaction if you have a sensitivity. Some brands may use a corn-derived coagulant for the curd, which would cause a reaction in anyone with a corn allergy. There also is a possibility that the tofu may become contaminated with other allergens during the manufacturing process.
The low cost and versatility of soybeans has made them a widespread ingredient in industrial food production. If you've recently become aware of a soy allergy from eating tofu, learning which foods to avoid because of soy can be a significant challenge. Aside from obvious soy products such as miso and soy sauce, such generic-sounding ingredients as natural flavor, vegetable broth, vegetable gum or hydrolyzed vegetable protein are frequently soy-derived. Even some medications contain soy. If you are uncertain whether a product is soy-free, contact the manufacturer directly with your questions.