Red kidney bean toxins

Red kidney beans form part of the pulses family (which also includes peas and lentils) and are available in both dried and tinned versions. They are often used in recipes such as chilli con carne.

These and other types of beans are considered healthy and nutritious but there is a downside to this. The downside is that they are also capable of causing food poisoning.

Causes of red kidney bean poisoning

The main cause is a toxin called ‘phytohaemagglutinin’ or kidney bean lectin. This is a sugar based protein (glycoprotein) which is found in many types of beans which includes cannellini beans and broad beans.

But some of the highest concentrations of this toxin are found in red kidney beans.

This toxin is killed if red kidney beans are cooked at a high enough temperature and for the right length of time. It is also important that red kidney beans are prepared correctly before use which means soaking them for at least 8 hours before hand.

But if they are cooked for shorter periods of time or at lower temperatures such as those in slow cookers then this will be insufficient to kill this toxin.

Undercooked red kidney beans are more toxic than raw kidney beans.

Symptoms of red kidney bean poisoning

These symptoms appear around 2 to 3 hours after the kidney beans have been eaten. However, it only takes a few beans to cause the following symptoms:

• Nausea
• Vomiting
• Diarrhoea
• Abdominal pains

These symptoms appear soon after consumption but, they also disappear quickly as well.

How is this diagnosed?

A diagnosis will be made via a physical examination, these symptoms and the types of foods that have recently been eaten.

Treatment for red kidney bean poisoning

Most cases resolve themselves within a few hours. But there have been cases which have required admittance to hospital. This is usually been due to the quantity of beans consumed and dehydration.

Persistent vomiting or diarrhoea can result in a depletion of fluids, and electrolytes which need to be replaced. This can be done at home via an ‘oral re-hydration’powder which can be purchased at a local pharmacy.

But serious cases of dehydration will require fluid replacement via an intravenous drip.

Preventing red kidney bean poisoning

This type of food poisoning occurs as a result of consuming raw or undercooked kidney beans. So in order to prevent this from happening, take the following precautions:

• Soak the red kidney beans for up to 8 hours. This can be done overnight if you prefer.
• Drain and rinse these beans. Throw this water away
• Put these beans in a pan of cold water and bring to the boil
• Boil them for at least 10 minutes to destroy the toxins
• Simmer them for 45 minutes to an hour

If these beans are still hard in the centre then cook them for longer until they have softened.

Follow any cooking instructions carefully and do not be tempted to shorten the cooking time.