Why Are Lima Beans Poisonous?

Lima beans also known as butter beans are a delicious and nutritious vegetable that is a staple in many cuisines around the world. However, raw or undercooked lima beans contain a natural toxin that can be harmful if consumed in large quantities. In this article, we’ll explore why lima beans are poisonous and what you need to know to enjoy them safely.

Lima Beans Contain Cyanogenic Glycosides

The reason lima beans are poisonous is that they contain compounds called cyanogenic glycosides. These substances are found in over 2500 plant species including cassava, almonds, bamboo shoots, and lima beans.

Cyanogenic glycosides are part of the plant’s natural defense system. When plant tissues are damaged, like during chewing, enzymes are activated that break down the cyanogenic glycosides into hydrogen cyanide, which is extremely toxic even in small doses.

So in lima beans the main cyanogenic glycoside present is called linamarin. When linamarin comes into contact with the enzyme linamarase either from chewing or during digestion, it produces hydrogen cyanide.

Small Amounts of Cyanide in Lima Beans

The good news is that commercially grown lima beans in the United States contain relatively low levels of linamarin, around 100-170 mg of cyanide per kg. Compare this to wild lima beans which can contain over 1000 mg per kg!

As long as lima beans are properly prepared, the small amount of cyanide present is not harmful for human consumption. Our bodies can easily detoxify small doses of cyanide, as long as lima beans are not the only food source and dietary protein intake is adequate.

Proper Cooking Neutralizes Cyanide

Cooking lima beans destroys the linamarase enzyme so that the cyanide cannot be released. Different cooking methods have varying effectiveness at reducing cyanide content:

• Boiling for over 30 minutes removes around 80% of cyanide
• Soaking beans for 24-48 hours, draining soaking water, then boiling briefly leaches out cyanide
• Steaming is less effective than boiling

There is limited research on cyanide removal for specific home lima bean recipes. However, experts recommend boiling or steaming for at least 5-10 minutes, which should neutralize most of the cyanide in fresh lima beans.

Safe Enjoyment of Lima Beans

When consuming lima beans, follow these tips for safe enjoyment:

• Soak beans overnight, drain water, and rinse before cooking
• Boil or steam lima beans for at least 10 minutes
• Do not eat raw or undercooked lima beans
• Eat lima beans in moderation as part of a balanced diet
• Avoid eating only lima beans for extended periods
• Ensure adequate protein intake from other foods like meat, dairy, eggs

With proper preparation, lima beans are a tasty and nutritious legume that provides protein, fiber, iron, and other vitamins and minerals. The small amount of natural cyanide can be easily neutralized through cooking. Just be sure to fully cook lima beans and eat them as part of a varied diet for safe and healthy enjoyment of this versatile veggie.

Frequently Asked Questions

Why are raw lima beans poisonous?

Raw lima beans contain linamarin, a cyanogenic glycoside that can release hydrogen cyanide when chewed or digested. Cooking neutralizes the enzyme so cyanide cannot form.

Are canned lima beans poisonous?

Properly canned lima beans are safe to eat. The canning process involves boiling which destroys the enzyme that produces cyanide. Always cook canned beans before eating.

Do all legumes contain cyanide?

Some other legumes like cassava, bamboo shoots, and almonds also contain cyanogenic glycosides. But proper processing and cooking neutralizes the toxin in all of these foods.

What happens if you eat raw lima beans?

Eating just a few raw lima beans is unlikely to cause illness. But consuming very high quantities of raw lima beans could potentially be fatal due to cyanide toxicity. Always cook lima beans thoroughly before eating.

Can you eat lima bean sprouts raw?

No, lima bean sprouts could still contain toxic cyanide. It’s safest to cook lima bean sprouts before eating them to destroy any enzymes that could create cyanide.

How much cyanide is toxic?

Cyanide toxicity depends on the size of the dose. Consuming over 5-10 mg per kg of body weight at one time could be fatal. But the cyanide in properly cooked lima beans is not a toxic risk.

Do you have to soak lima beans before cooking?

It’s recommended to soak lima beans in water for 24-48 hours before cooking. Soaking helps leach out some of the natural toxins. Discard the soaking water and rinse beans before cooking.

What is the shelf life of cooked lima beans?

Cooked lima beans will last 3-5 days refrigerated and 6-12 months frozen. Always store cooked lima beans in airtight containers. Discard beans if mold develops. Reheatcooked beans to 165°F before eating.

Can dogs eat lima beans?

Cooked lima beans are safe for dogs to eat in moderation. But dogs should not eat raw lima beans as they are also susceptible to cyanide poisoning. Introduce lima beans slowly along with the dog’s regular diet.

The Bottom Line

Lima beans contain a small amount of natural cyanide. But with proper preparation by soaking, boiling, steaming, canning, or cooking for at least 10 minutes, the lima beans become perfectly safe and healthy to eat. Enjoy lima beans in balance with other foods as part of a varied diet. Follow basic cooking methods to neutralize toxins so you can reap the many nutritional benefits of this nutritious legume.