Not so fun fact: Did you know that eating soaked raw or undercooked beans can result in food poisoning? It can. The culprit is a plant lectin known as phytohaemagglutinin, or simply, hemagglutinin, a chemical known to cause agglutination of mammalian red blood cells and to disrupt cellular metabolism.

According to the U.S. Food and Drug Administration, phytohaemagglutinin is found in many types of beans, however, red kidney beans contain the highest levels of hemagglutinin. White kidney beans contain a third as much of the toxin while broad bean varieties contain only 10% as much hemagglutinin as red kidney beans. That's still plenty, however, since you only need to eat four or five undercooked red kidney beans to get sick.

Bean Poisoning Symptoms

Symptoms start to appear within one to three hours after consuming the beans. They include nausea and vomiting followed by diarrhea and, in some cases, abdominal pain. Although the symptoms may be severe enough to warrant hospitalization, they resolve spontaneously within a few hours. Everyone is susceptible, regardless of age, gender or other factors.

Preventing Bean Poisoning

It is easy to prevent bean poisoning. The recommended procedure is to boil soaked raw beans in water for a minimum of 10 minutes. It is important that the water reach boiling or 100 degrees Celcius (212 degrees Fahrenheit), since exposing the compound to 80 degrees Celcius (176 degrees Fahrenheit) actually increases its toxicity about five times.

Share Your Experience

Had you ever heard of hemagglutinin in beans or bean poisoning? Have you ever experienced this type of food poisoning? Here are replies from readers:

"I never knew about kidney bean poisoning until today! I made vegetable soup with dried bean mix (without soaking) in a Crockpot. The soup didn’t cook thoroughly even though it was on for over eight hours. Fortunately, my symptoms were mild —but still a very unpleasant experience." —Lea

"Here’s the drill, folks! Legumes have been a staple of humans and other critters for a long, long time. Look in any old cookbook (mine date back over a century) and guess how they prepared them. THEY SOAK THEM OVERNIGHT AND BRING TO A BOIL, THEN SIMMER UNTIL TENDER. Obviously, they only had fire for fuel and no electricity. I never knew about PNG until last year and have prepared many types of beans, including dry red beans. My main goal is to greatly reduce polysaccharide sugars which encourage anaerobic activity in the gut and, guess…gas!

So, after 50 years of cooking and research, here's the magic recipe:

• Sort, rinse, and cover 1 lb. of beans with 2 inches of water. Add 4 tsp. of salt.

• Soak overnight or 6 to 8 hours.

• Bring to a boil, and boil 2 minutes.

• Remove from heat, cover and soak 4 hours.

• Now, discard water and rinse the beans.

• Cover beans with water and bring to simmer.

• Cook until tender.

• Drain and serve.

Note: I use a pressure cooker (seven minutes at 15 lbs. for Pinto beans). Beans are an important part of my diet, almost every day!" —JVPETC

"I have this reaction to ALL legumes. It doesn’t matter how they are prepared or cooked. It also doesn’t seem to matter how little I consume. I have become extremely ill after consuming something that was made with a small amount of soy flour. I have also started to have a similar reaction to certain nuts.

One of my frustrations is that soy seems to be a standard substitution in so many foods, and isn’t always listed. I read that if an ingredient is a common substitution (soy grits for corn, for example) that the substitution isn’t always listed. It is to the point that I can no longer eat foods that my family doesn’t make from “scratch” with known ingredients." —Paula

"I am so glad I found this site after waking up at 3:30 a.m. this morning with intestinal pain, nausea, diarrhea and feeling like I was about to pass out right on the bathroom floor. I had eaten dark beans I made from scratch in the crockpot two nights in a row. It was frightening because I couldn’t come up with a reason why this happened. Now I know." —Laurene

"I’m just getting back to normal after two pretty awful days. My girlfriend made us a pinto bean and pumpkin casserole and three hours later I felt the first wave of nausea. An hour later I was projectile vomiting until I was just retching. I don’t think I’ve ever felt so ill before. The pinto beans had been soaked overnight and boiled as the instructions said to, but there must have been a few that didn’t cook properly. My girlfriend was absolutely fine and thankfully so is our baby, who had some mashed up. I had to take two days off work and have only just started back on solid food as I couldn’t stomach anything but water." —Jon

"I just wrote to a major cooking magazine about the possibility of hemagglutinin poisoning from two slow cooker recipes they printed that called for uncooked navy beans. They answered that they had researched their recipes with the FDA and were told there was very little danger in using the recipe, as most such poisoning comes from red kidney beans. Have they gone bonkers or just don’t want to admit they printed recipes that could make people sick?" —Jessica Deforest

"I just ate some romano beans and I’ve never really cooked beans before so I didn’t know I had to soak and then cook them, I just cooked them. I threw out most of my dish but ate a significant portion of the meal. My stomach feels a bit weird so I guess I might get sick, but hopefully, it’s just a psychological reaction to learning about this, or it’s just that the beans are tough to digest because of my flawed cooking. Wish me luck.

—Jaime Silta

"My adult son has just had a horrendous episode of acute poisoning that was incredibly intense. Luckily, he has excellent health generally. After eating a plate of shop bought ready prepared falafel with hummus, he was fine for three or four hours and then had a rapid onset of acute abdominal pain and diarrhea. He also had some blood loss with diarrhea. The pain was really severe and at one point I thought I would have to get an ambulance. He also began vomiting. Incredibly, this really severe and acute illness began to wear off after four or five hours. 20 hours later, he is feeling fine again, although obviously exhausted! I have always thought that the most severe food poisoning was associated with contaminated meat and dairy products and had no idea that beans could be so lethal!" —Cate

"I ate raw Romano beans I bought from the grocery store. They sold them beside the green beans that I’ve always eaten raw, so I thought it was just another type of bean. I ended up eating an entire bag of them, thinking they were good. BIG MISTAKE. I felt like throwing up five minutes later. They burned in my stomach. Went to bed, passed a lot of gas, my intestines were spasming. Woke up 6 hours later with abdominal pain. Drank Pepto Bismal. Went back to bed. Woke up an hour and a half later with extremely watery diarrhea. Had to pass water for stool several times." —Anonymous

"My wife has just had a severe attack of vomiting and diarrhea. The suspect is the falafel we had for dinner made from white butter beans, or dried runner beans. The recipe used from Claudia Roden’s book specifies making the rissoles from uncooked beans. They are then deep-fried. I found a 2008 article from the Independent called "Beware of the Beans." A family using the same recipe (shallow fried, however) all came down with severe symptoms. Even white beans have enough lectin to cause problems." —Jeremy Cunningham