Eating as few as 4 beans can be toxic—unless you cook them correctly. Find out how to cook dried kidney beans safely to get rid of the toxin and stay healthy.

moms chili

Pictured Recipe: Mom's Chili

Dried red kidney beans may be one of your pantry staples. And why not? They're packed with protein, fiber and iron, and incorporating them into your diet can offer a bevy of health benefits, from lowering your cholesterol to reducing your risk of a heart attack. They pack a real health punch.

But it turns out that red kidney beans also have a dark side: They can be toxic-when they're not cooked correctly, that is. Research from the U.S. Food and Drug Administration shows that dried red kidney beans contain a particular lectin (a type of protein) that is toxic to people. To rid the kidney beans of this lectin, they have to be boiled for at least 10 minutes.

But if you're cooking them in a slow cooker, chances are they're not reaching the required 212°F to rid the beans of their toxicity. And you could get sick from them, according to the FDA.

Phytohaemagglutinin (PHA), the lectin in red kidney beans, defends legumes against pests and other destructive pathogens. But in humans, eating as few as four beans with PHA can cause vomiting, diarrhea and gastrointestinal illness, the FDA says.

How to Safely Cook Dried Red Kidney Beans

Luckily, those symptoms usually ease in as few as three hours-but wouldn't it be better to avoid them altogether? You can, by cooking the beans properly.

1. Soak the Dried Beans

First, raw kidney beans should be soaked in water for 5 hours or, even better, overnight.

2. Boil the Soaked Beans

After soaking, drain the beans, and then boil them (so the water reaches 212°F) in fresh water for a minimum of 10 minutes.

3. Prepare as Desired

Once the beans have been cooked this way, you can be assured the toxic lectin has been released and they're safe to prepare for your meal, in a slow cooker or another way.

Are Other Beans Safe?

Before you boil every bean in your pantry, take heart: while most dry beans contain PHA, they don't have nearly as much as red kidney beans. According to a report from Ohio State University's College of Food, Agricultural and Environmental Sciences, other beans (including white kidney beans and cannellini beans) have only about one-third as much PHA as red kidney beans, while fava beans have just 10 percent of the PHA content that red kidney beans do. So you can continue to eat most beans without worry.

And if you're using canned kidney beans in a slow-cooker chili, don't worry-they've already been cooked.

Watch: How to Make Southwestern Three-Bean & Barley Soup