Are Red Kidney Beans Toxic?
Why slow-cooking dried red kidney beans isn't safe.
There are many things you may read online and wonder if they’re really true. In July 2020, it was reported that red kidney beans were linked to food poisoning of 45 people. This report can certainly leave you confused as to how a food eaten regularly be linked to food poisoning? Here’s what you need to know to keep you and your loved ones safe.
The Toxin in Red Kidney Beans
Legumes including beans, peas, and lentil and grain products have high amounts of a natural compound called lectins. Some of the functions of lectins include the ability to bind to and clump together red blood cells. Lectins also interfere with nutrient absorption from the intestines.
The FDA’s “Bad Bug Book” explains that the lectin phytohaemagglutinin has toxic effects in human when consumed in high levels. Red kidney beans have the highest levels of it. The unit to measure the toxins is called hemagglutinating unit (hau). Raw kidney beans have between 20,000 to 70,000 hau, while fully-cooked beans contain 200 to 400 hau. White kidney beans have one-third the amount of the toxin compared to red kidney beans and broad beans have 5 to 10-percent that of red kidney beans.
What Happens When You Eat the Raw Red Kidney Beans?
Toxicity occurs when you eat raw, soaked kidney beans either alone or in salads or casseroles. There have also been reports of toxicity when cooking raw, dried kidney beans in a slow-cooker.
Just four or five raw kidney beans can trigger the symptoms of toxicity. Within one to three hours of consumption of the raw beans you can experience extreme nausea and vomiting, with diarrhea and abdominal pain developing afterwards. The toxicity does not result in death and recovery is usually rather quick within three to four hours after onset of the symptoms. Some cases have required hospitalization.
What You Should Know to Prevent Illness
Cooking your beans to the proper minimal internal cooking temperature will destroy most of the harmful toxins in it, making it safe to eat. Our bodies can tolerate a small amount of them, but not the amount found in raw kidney beans.
Studies conducted by British scientists have found that you should soak red kidney beans in water overnight, discard the water, and then boil the beans in new water until they boil at 212 degrees F for at least 10 minutes. Dishes cooked in slow cookers, like casseroles, do not reach this temperature and that is why it’s been linked to toxicity. The toxicity only applies to raw dried or soaked raw kidney beans. There are no toxicity issues when it comes to canned red kidney beans since they are pre-cooked.
Toby Amidor, MS, RD, CDN, is a registered dietitian and consultant who specializes in food safety and culinary nutrition. She is the author of The Greek Yogurt Kitchen: More Than 130 Delicious, Healthy Recipes for Every Meal of the Day.
*This article was written and/or reviewed by an independent registered dietitian nutritionist.