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Lectins are naturally occurring proteins that occur in varying amounts in most plant foods.

iStockPhoto / Getty Images

The question

I’ve read that it’s not healthy to eat beans and lentils because they’re high in lectins. Is this true? What are lectins?

The answer

Forget about wheat or gluten. There’s a new dietary evil we’re being told to avoid: lectins.

Lectins are particularly abundant in lentils, beans (e.g., kidney beans, black beans, chickpeas) and whole grains – nutrient-packed foods associated with many health benefits.

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It’s widely claimed that lectins can cause a litany of health problems, including inflammation, brain fog, weight gain, high cholesterol, rheumatoid arthritis, allergies and cancer. Eating a lectin-free diet, promoted by cardiologist Steven Gundry in his book The Plant Paradox, is said to prevent and in some cases even cure these and other illnesses.

Before you drop lectins – and a swath of nutritious foods – from your diet, here’s what you should know.

What are lectins?

Lectins are naturally occurring proteins that occur in varying amounts in most plant foods. Besides pulses and grains, which have the highest amount of lectins, lectins are found in fruits, vegetables, soybeans, peanuts, nuts, coffee, chocolate, certain herbs and spices and milk.

Lectins act as a defense mechanism for plants, protecting them from invaders such as microbes, insects and animals. The same mechanisms used to shield plants from danger is thought to cause problems when lectins are consumed by people.

Do lectins cause harm?

Lectins are not digested, or broken down, in our gut. As a result, these proteins are able to attach to carbohydrate components of cells that line the digestive tract.

Lectin-free diet advocates contend that lectins can seep through the gut lining and bind to sugar molecules throughout the body. In so doing, lectins can disrupt your immune system and wreak havoc on your health.

Experiments conducted in mice fed raw beans or isolated lectins have demonstrated that lectins damage the gut. Animal studies also suggest that active lectins can block the absorption of minerals such as calcium, iron and zinc.

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And eating raw or undercooked kidney beans, especially red ones, causes nausea, vomiting and diarrhea in people. Red kidney beans have a very high concentration of phytohaemagglutinin, a lectin that causes red blood cells to stick together.

The notion, however, that eating plant foods with lectins causes numerous chronic health conditions isn’t backed by scientific evidence. Limited research has been conducted on the harmful effects of lectins in humans, or the amount that’s consumed in a typical diet.

Cooking inactivates lectins

Raw beans contain active, potent lectins. But it would be rare to consume a high amount of active lectins since we don’t eat beans (or grains) in their raw form.

Once beans are soaked and boiled for 30 minutes, most lectins are inactivated. Canned beans have already been cooked, so they’re low in lectins.

Don’t use a slow cooker to cook raw beans, though, as it likely won’t get hot enough to destroy lectins. Research indicates that the protein is inactivated when boiled at 212 degrees Fahrenheit.

Sprouting beans and whole grains also deactivates lectins.

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Bottom line

For most people, there’s no reason to avoid nutritious plant foods simply because they contain lectins.

There’s plenty of evidence that eating a diet rich in whole grains, beans, lentils, fruits and vegetables offers protection from high blood pressure, heart disease, stroke, Type 2 diabetes and colorectal cancer. The well-documented health benefits attributed to these foods outweigh the potential harm from the lectins in them.

That said, some people may be sensitive to lectins, especially people with underlying digestive issues.

If you suspect certain lectins might bother you, consider trying a short-term elimination diet with the help of a dietitian. Such an approach removes foods high in lectins for a few weeks and then reintroduces them, one at a time, to determine if symptoms return.

And for people who use dried beans, be sure to soak them in water for at least five hours, drain the water and then thoroughly cook by boiling or pressure cooking.

Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.

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