The Case Against Beans and Other Foods Containing Toxic Lectins

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By Dr. Mercola

While whole foods are healthy, there are certain caveats to consider even here. Lectins (not to be confused with the phospholipid lecithin) are carbohydrate-binding proteins that are widespread in the plant kingdom. An estimated 30 percent of fresh foods contain lectins.1

Even dairy contains lectins. Grass fed butter is an exception. Grass fed milk is also lower in lectins than grain-fed milk, thanks to higher amounts of SlgA, an immunoglobulin that binds to lectins.2 Lectins get their name from the Latin word legere, from which the word “select” derives — and that is exactly what they do: They select (attach to) specific biological structures that allow them to do harm, as part of the plant’s self-defense mechanism.

It’s nature’s ingenious way of keeping natural enemies like fungi and insects at bay. Unfortunately, some of these glycoproteins may also cause trouble in humans.
Lectins were first discovered in castor bean casings, which contain the lectin ricin. Ricin is so toxic that a dose the size of a few grains of salt can kill an adult if injected or inhaled.

The Plant Paradox

Dr. Steven Gundry’s newly released book, “The Plant Paradox: The Hidden Dangers in ‘Healthy’ Foods That Cause Disease and Weight Gain” has gained widespread media attention, reigniting the discussion — and concern — about lectins.3,4 Gundry has also completed a human study on lectins. In the Selfhacked interview above, he discusses some of his findings, and the reasoning behind his lectin avoidance diet.

There’s a load of interesting information there, so I recommend taking the time to watch it, and/or read through the accompanying article.5 Many are now familiar with the problems of gluten, but lectins could potentially be just as problematic. That’s not to say the issue lacks controversy. There’s plenty of that to go around. Still, I believe the issue of lectins — toxic lectins, to be more exact — in the diet warrants a closer look.

While Gundry goes so far as to declare lectins the greatest danger in the American diet, especially for those with autoimmune disease, the reality is likely to be far different. Authority Nutrition6,7 points out that lectins in small amounts can actually provide valuable health benefits, including immune and inflammation modulation, and that problems will only arise when you’re getting high amounts of them.

Indeed, I believe it would be a mistake to assume all lectins are bad for you. For example, avocados contain the lectin agglutinin (persea Americana agglutinin),8 but that hardly places them on the list of foods to avoid! Avocados are among the healthiest foods I can think of, and research9 shows the agglutinin found in avocado is devoid of specificity for carbs. It interacts with proteins and polyamino acids instead.

Beans, on the other hand, not only contain lectins that can cause problems for many people, they also have the added drawback of being high in net carbs, and are therefore best avoided in the initial transitional stages of a ketogenic diet. So, there are pros and cons to consider, depending on the food in question. The presence of lectin is by no means a sole determinant. That said, certain lectins have more potent toxic or allergenic effects,10 and the lectins found in beans fall into this category.

Lectins and Their Harmful Effects

Among the most problematic lectin-containing foods11,12 are wheat and other seeds of the grass family,13 beans, soy and other legumes, peanuts, and members of the nightshade family14 such as eggplants, potatoes, tomatoes and peppers.

Grains and legumes such as black beans, soybeans, lima beans, kidney beans and lentils contain the highest amounts. Generally speaking, lectins are a type of glyca-binding protein, meaning proteins that bind to carbohydrates in your body. There are many types of lectins, and the main difference between them is the type of sugar each prefers and binds to in your body.

As noted by Dave Asprey, founder of,15 “One of the reasons wheat is so bad for you is that the lectin in wheat is attracted to glucosamine, the polysaccharide that covers your joints.” Some — including wheat germ agglutinin (WGA), found in wheat and other grass-family seeds — bind to specific receptor sites on your intestinal mucosal cells and interfere with the absorption of nutrients across your intestinal wall.

As such, they act as “antinutrients,” and can have a detrimental effect on your gut microbiome by shifting the balance of your bacterial flora — a common precursor to leaky gut.

Lectins Are Highly Inflammatory

One major concern is that most lectins are proinflammatory, meaning they trigger inflammation and create advanced glycation end products. C-reactive protein (CRP) is one example of the many lectins you have circulating in your body right now, and it’s used as a marker of inflammation.

They are also immunotoxic (capable of stimulating a hyperimmune response), neurotoxic and cytotoxic, meaning they’re toxic to cells and may induce apoptosis (cell death). Certain lectins may also increase your blood viscosity by binding to your red blood cells.

This makes the blood cells sticky, resulting in abnormal clotting. Some lectins (such as WGA) may even interfere with gene expression and disrupt endocrine function. Lectins also promote leptin resistance, thereby increasing your risk of obesity. All of these factors can predispose you to disease.

Who Should Avoid Beans and Other Lectin-Rich Foods?

People who may need to be particularly careful with lectin-containing foods — specifically those in the nightshade family, all grains, legumes and beans — include those struggling with inflammatory or autoimmune conditions,16,17 including but not limited to:

Caution may also be warranted if you’re taking nonsteroidal anti-inflammatory drugs, as they’ve been shown to increase gut permeability.18 This allows toxic lectins to enter your bloodstream, thereby raising your risk of experiencing an adverse reaction.

Avoid Beans During Initial Stage of Ketogenic Diet

Foods high in both net carbs (total carbohydrates minus fiber) and lectins deliver double the harm, and this includes grains and beans. In fact, I recommend abstaining from both grains and beans during the initial stages of my metabolic mitochondrial therapy (MMT) program, which involves cyclical nutritional ketosis, detailed in my new book, “Fat for Fuel.”

Once you’re through the initial stage where strictly limiting net carbs is crucial, and your body is efficiently burning fat for fuel, then beans (and other net carbs such as grains) can be reincorporated, especially during your “feasting” days. Feast-and-famine cycling or pulsing is an important component of the MMT program. This simply means you cycle in and out of nutritional ketosis rather than staying in ketosis indefinitely.

Initially, you limit your intake of net carbs to 40 or 50 grams per day and replace them with healthy fats. This will transition your body into primarily burning fat for fuel and radically reduce your risk for most chronic diseases. If your insulin level is below 3, then your carbohydrate consumption may be ideal for you even if it’s higher than 40 or 50 grams. However, if your insulin level is higher, then you are best advised to scale back net carbs from your diet.

The higher your insulin levels are, the fewer carbohydrates you should eat. Unless your fasting insulin is below 5, avoid carbs like beans, legumes and grains such as rice, quinoa and oats in this initial phase. These foods not only drive your insulin levels up but also increase your chances of becoming leptin resistant, which interferes with your ability to lose weight.

Once your body is burning fat for fuel, you then begin cycling in and out of ketosis. As a general rule, I recommend increasing your net carbs and protein one or two days a week — days on which you can go as high as 100 grams or more of net carbs — and then cycling back into ketosis on the remaining five or six days. During these high-carb days, beans are acceptable if you like them. Just be sure to cook them properly to neutralize most of the lectins.

Why Beans Must Be Carefully Cooked

Red kidney beans contain the highest amounts of the toxic lectin phytohaemagglutinin. Many other beans also contain it, albeit in lower amounts, including white kidney beans and Greek butter beans. This lectin is why you should never eat beans raw or undercooked, lest you come down with bloody vomiting and other symptoms reminiscent of severe food poisoning. As few as five undercooked beans can cause severe symptoms.

Cooking at high heat deactivates this lectin, making the beans safe to eat. Research has shown cooked red kidney beans contain only 200 to 400 hemagglutinating units (hau), compared to the 20,000 to 70,000 hau found in the raw beans. While most people would never consider eating dry beans without cooking them, skipping steps or undercooking them are common kitchen faux pas that send many to the hospital. As noted in The Atlantic:19

“Stories of lectin poisoning are not especially rare. In ‘The Independent’20 the food writer Vicky Jones describes a dinner party in which she used Greek butter beans in a dish without boiling them first. Soon everyone was violently ill. It came on so quickly that before they could consider going to the emergency room, death seemed preferable to [trekking to the] hospital. Jones recovered fully, as most lectin-poisoned people do.”

General Cooking Recommendations and Other Lectin-Reducing Strategies

Here are some general preparation and cooking guidelines to reduce toxic lectins in beans:

Soak the beans in water for at least 12 hours before cooking, frequently changing the water. Adding baking soda to the soaking water will boost the neutralization of lectins even further21

Rinse the beans and discard the water used for soaking

Cook for at least 15 minutes on HIGH heat. Cooking beans on too-low a heat can actually increase toxicity levels up to five times or more.22 Avoid any recipe calling for dry bean flour, as the dry heat of your oven will not efficiently destroy the lectins

The best way to destroy lectins is to use a pressure cooker.23,24,25 Many swear by the InstaPot,26 a multipurpose pressure cooker. Avoid slow cookers, as they will actually increase lectin content due to the low temperature used.

A study27 that compared the phytic acid content of soaked peas that were then either boiled regularly or cooked in a pressure cooker found pressure cooking reduced phytic acid content by 54 percent, compared to 29 percent through regular boiling. Pressure cooking may also preserve more nutrients than other cooking methods

Sprouting and fermenting will also dramatically reduce the lectin content of foods that contain it, making them far safer. This is one of the reasons why traditionally sprouted grain bread is easier on your digestion than conventional bread made with processed, unsprouted grains.

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