Red kidney beans, although safe to eat when properly cooked, should not be eaten raw or partially cooked, because of the naturally occurring toxin Phytohaemagglutinin. Kidney beans belong to the bean genus within the pea family, according to the U.S. Department of Agriculture. This versatile bean lends itself well to both main and side dishes and offers you a wide range of nutrients.
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Phytohaemagglutin, which the U.S. Department of Agriculture, or USDA, refers to as kidney bean lectin, occurs naturally in many other types of beans. However, the red kidney bean holds the distinction for the bean with the highest concentration of this dangerous toxin. The toxin, measured in hemagglutinating units, or hau -- a measure of toxicity -- falls from a high of 70,000 hau in raw beans to under 400 hau when you thoroughly cook the red kidney beans. Unfortunately, you do not have to eat very many beans to get sick, as it only takes eating four or five raw or undercooked beans before symptoms begin.
The symptoms of consuming kidney bean lectin include extreme gastrointestinal upset with nausea and vomiting often beginning within a few hours of consumption. Other symptoms include diarrhea and stomach pain. Fortunately, the USDA reports that most people recover rapidly and without the need for hospitalization. If you develop these symptoms after eating an undercooked or raw kidney bean, call your doctor and ask for his treatment recommendations.
Even slightly cooked red kidney beans can cause illness, as evidenced by information in a foundational analysis published in 1990. The study, published in the July 1990 edition of the journal "Epidemiology and Infection" found that eating both raw beans and those inadequately cooked on the stove or in a slow cooker could cause illness. The study found that if you soak the beans overnight to soften them, and then boil them for a minimum of 10 minutes, the toxin drops to an acceptable and safe level. Avoid cooking the beans at a low temperature, as a bean cooked at 180 degrees Fahrenheit can still be toxic.
As long as you cook the red kidney beans thoroughly and boil them for 10 minutes, you do not need to avoid consuming this healthy bean. Avoid using a crockpot, and cook the beans on the stove instead to ensure the beans do not simmer at a relatively low temperature and thus fail to come to a complete boil. Keep raw beans away from young children, who may not understand that eating a raw bean may be dangerous. Use kidney beans in salads, with basmati rice, in chili or served as a side dish.