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Raw Kidney Beans

I read that kidney beans are harmful when eaten raw. Several day care and nursery schools have dry beans (different varieties) out for kids to play with. What danger would there be if a child ate a few of these raw beans?

Answer - Red Kidney Bean Poisoning is an illness caused by a toxic agent, Phytohaemagglutnin (Kidney Bean Lectin). Different types of lectins are found in many species of beans, but are highest in concentration in red kidney beans. The unit of toxin measure is the hemagglutinating unit (hau). Raw kidney beans contain from 20,000 to 70,000 hau, while fully cooked beans contain from 200 to 400 hau. White kidney beans, another variety of Phaseolus vulgaris, contain about one-third the amount of toxin as the red variety; broad beans (Vicia faba) contain 5 to 10% the amount that red kidney beans contain.

As few as 4 or 5 kidney beans can bring on symptoms within 1 to 3 hours. Symptoms include extreme nausea, vomiting, diarrhea, and abdominal pain. Some persons have been hospitalized, but recovery usually occurs about 3 - 4 hours after symptoms appear.

Lectins are inactivated with cooking so fully cooked or canned kidney beans are safe to eat. Undercooking may actually increase lectin activity and increase the hazard. This could be a problem when using slow cookers (crock-pots) if time/temperature conditions are not adequate to fully cook the beans. Therefore, when kidney beans are called for in slow cooker recipes, make sure they become fully tender, or use pre-cooked or canned beans rather than raw beans.