Red kidney beans contain a potent toxin called phytohaemagglutinin which can cause severe gastrointestinal symptoms, including nausea, vomiting, and diarrhea. Fortunately, this toxin is deactivated by the heat of boiling. So boiled kidney beans, and this includes canned beans, are perfectly safe. But slow cooking uses lower temperatures than boiling, which is 212 degrees Fahrenheit. The actual temperature reached in a slow cooker varies by model and the setting used, but it is always below boiling-this is the very definition of slow cooking! Thus, the toxin in kidney beans will not be deactivated, at least not fully, by slow cooking.
