How I Accidentally Poisoned Myself on Slow-Cooked Red Kidney Beans
I’m Indian, so the red kidney bean (or rajma) is a staple in our pantry. Rajma chawal, or rice with red kidney beans, is a homemade comfort food enjoyed by many cultures on a lazy rainy afternoon. It’s a simple recipe that requires beans that have been soaked overnight and rinsed, a few Indian spices and masala powders, and a pressure cooker. Toss the soaked beans into the pressure cooker, add fresh water and allow the whistle to go off 5 or 6 times (“cook for 6 whistles” as my dad says). Fry off with spices, add on rice, and serve.
I’ve never gotten sick from red kidney beans till yesterday, and here’s what I did wrong, what happened and what I learned.
I used a slow cooker instead (big mistake)
Back home, the pressure cooker is a ubiquitous presence in every household. It’s pretty common to hear your neighbors’ pressure cooker go off when you are doing your lunch prep. But in my neighborhood in Toronto, it’s a quiet place, and using a pressure cooker (and five whistles no less) would cause quite a racket. So, I opted to use a slow cooker instead. I soaked my red kidney beans overnight, drained the water, rinsed it twice, added it to the slow cooker, and set it on high for about 4 hours. I then drained the water, dried the beans with a paper towel, and then stir-fried it with some spices. I ate them with some rice and went about my business. Three hours later, the trouble started.
The Unpleasantness
At about 10 pm, I knew something was amiss, and that was putting it mildly. Nausea hit me and sent me running to the washroom. Fortunately, I did not throw up. Then came unbridled diarrhea that felt like an upside-down juice box squeezed. This was followed by cramps and later by abdominal pain. I knew at this point that this was food poisoning. I immediately thought of the sandwich my friend and I ate at a Downtown cafe earlier that morning. That had lettuce on it; probably bacterial contamination? But we both had the same sandwich, and when I texted him, he said he was feeling right as rain. So that ruled out the sandwich hypothesis. Wait a minute, could it have been the kidney beans? But it’s vegetarian — you didn’t have the threat of undercooked meat to fret over. But the curiosity got the better of me, and I looked it up online. And that’s when I realized that I inadvertently poisoned myself.
The culprit: lectin phytohaemagglutinin
Lectins are proteins that bind to carbohydrates. Red kidney beans contain a specific lectin called phytohaemagglutinin (PHA). PHA, in turn, is comprised of leucoagglutinin (PHA-L) and PHA-E. The former causes white blood cells to clump and the latter red blood cells. In a rat model, the oral administration of PHA led to a blocking effect on epithelial endocytosis; in other words, a blocking effect on the cell’s ability to transport molecules by engulfing it with its membrane. Red kidney beans are particularly scary because they have the highest content of PHA among beans — 20,000 to 70,000 hemagglutinating units. So why haven’t we all keeled over from a bowl of spicy rajma chawal?
As with all proteins, high temperatures denatures them. Think of a raw egg and how the yolk cooks as the boiling point hits. Similarly, cooking the beans reduces the PHA content in red kidney beans to 200 to 400 hemagglutinating units. This amount of PHA can be handled by our intestines, although going overboard on that delicious chili can leave you with some unpleasant flatulence.
Slow cookers don’t make the cut in terms of heat
A peer-reviewed publication by Rodhouse et al (1990) discussed 50 suspected incidents of food poisoning in the UK from PHA poisoning caused by the consumption of raw or undercooked red kidney beans. What’s curious is the following statement in the introduction:
“Heating beans at a lower temperature is reported to result in an increase in levels of lectin, hence the observation that beans cooked at 82 °C (which were still palatable) were toxic whereas those cooked at 91°C were not.”
The internal temperatures of foods cooked in slow cookers reach about 75 °C, which is insufficient to degrade the PHA to tolerable levels. However, in a pressure cooker, the temperatures are high enough to cook the beans. When my dad said, cook for 6 whistles, he wasn’t kidding.
Recovery
Although the FDA’s “Bad Bug Book” says recovery is rapid, I’ve been out of sorts for a little more than a day. I’ve been eating cooked rice drizzled with coconut oil and drinking coconut water to restore some of the electrolytes lost from diarrhea. My stomach’s on a churl, and I’ve got a mild headache.
Important takeaways
- Red kidney beans have the highest levels of PHA lectin among beans. PHA has insecticidal activity.
- Do NOT eat red kidney beans that are raw, or soaked, or that are undercooked.
- Do NOT use a slow cooker to make red kidney beans; use a pressure cooker instead, or buy precooked, canned beans from the supermarket. Boiling soaked beans in a saucepan with fresh water for over 10 minutes is also acceptable.
- There is no mortality tied to red kidney bean poisoning reported thus far, but it is definitely unpleasant and can occasionally lead to hospitalization.
I’m definitely off rajma chawal for the rest of the month.
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