Dietary Lectins: What Are They and Should You Be Concerned?

Even foods that are good for your health may have some properties that make them less than ideal.

woman holding bowl of green beans

And some things that you eat are just plain bad for you.

Lectins are often cited as a property in foods that you should avoid.

However, it’s hard to completely stay away from something that’s found in much of the food that you eat.

Lectins are proteins, and they exist in significant amounts in about 30 percent of foods.

They are especially concentrated in grains and legumes.

If you often eat a lot of lectin-containing food and you’re lacking in the enzymes to digest lectins, these proteins may enter the bloodstream.

They may cause nutritional deficiencies and digestive problems. They can also damage the walls of the intestines (1).

Some believe that lectins are partially responsible for creating a “leaky gut” that leads to autoimmune disease.

Lectins aren’t as scary as some people make them out to be.

So how dangerous are dietary lectins?

While lectins can be somewhat harmful to your health, there are many ways to manage your intake. Read on for more insights.

Lectin Infographic

Want to use this infographic on your blog? Just copy and paste the code below!

What Are Lectins Anyway?​

Lectins are proteins that bind carbohydrates within the organism (2).

This can be helpful for encouraging particles at the molecular level to interact with one another.

It is also necessary for some physiological functions, but it can be harmful in some cases.

Imagine that the surface of any molecule has tiny hooks, like Velcro. Those are lectins.

If the right molecule comes along, it will attach itself to those lectins.

The lectins on the surface of E. coli cells select and stick to certain cells of the intestinal tract.

Viruses can attach to and enter certain cells with the help of lectins.

These proteins play various roles in normal physiological functions, but they have also been implicated in causing cavities, inflammatory bowel syndrome and celiac disease (3).

3 bunches of green beans

Fruits and vegetables that contain lectins are:

  • Tomatoes
  • Potatoes
  • String beans
  • Carrots
  • Zucchini
  • Carrots
  • Green peas
  • Soybean, mung bean and lentil sprouts
  • Cantaloupe
  • ​Grapes (especially the seeds)
  • Cherries
  • Pomegranates
  • Raspberries
  • Blackberries
  • Beans

Wheat germ also contains lectins, as do peanuts, dairy products, many types of beans, nuts and seeds, garlic, marjoram, allspice and mushrooms.

However, variation can occur from day to day and from plant to plant.

In addition, the lectins found in dairy, nightshades, nuts and seeds aren’t as bad for you.

Plants may contain lectins as a survival mechanism.

One of the reasons that it is necessary to soak and properly cook dried beans is to reduce their lectin levels (4).

For example, castor beans contain so many lectins that they are poisonous to most animals. This keeps the castor bean species going.

The lectin found in castor oil has even been synthesized as a poison called ricin, which is used in biochemical warfare (5).

Lectins aren’t all bad.

However, if you eat a concentrated amount, you could end up with digestive distress, and if you eat them frequently, you may end up with chronic illness.

KEY POINT: Lectins are proteins that target and bind carbohydrates

They are found in many foods, but they are more concentrated in grains and legumes.

Consuming a Lot of Lectins Can Be Detrimental

Humans don’t have the proper enzymes necessary to digest lectins.

As they pass through the stomach, lectins remain largely unaltered. 

When they reach the intestines, they can attach to the lining of the gut (6).

In one study that was conducted on rodents, lectins made it through the stomach and attached themselves to the small intestines.

They temporarily thickened the walls of the small intestines, affecting their ability to absorb nutrients.

They also changed the length and function of the entire digestive tract. 

These effects were mostly reversed upon elimination of lectin from the diet (7).

Lectins can enhance pancreas growth and increase the release of digestive enzymes (8).

Lectins make it difficult for the body to maintain its own cells.

Therefore, people with damage from lectins may experience more digestive problems. This may occur gradually (9, 10).

Phytohaemagglutinin are the most commonly studied lectins. Kidney beans are one of the main sources of these proteins.

If you eat raw kidney beans, you can experience major pain in your abdomen, diarrhea and vomiting.

These are symptoms of lectin toxicity (11).

In fact, one hospital offered free food to customers during a “healthy eating day” in 1988.

Eleven of the customers who had eaten a large number of kidney beans experienced extreme digestive distress that day (12).

However, you’re not likely to eat raw kidney beans.

If you purchase canned beans, they have been soaked and cooked prior to canning.

Dried beans must be prepared properly to destroy many of the lectins.

KEY POINT: Lectins can be a major stomachache. They are poisonous when consumed in large quantities.

Too Much Dietary Lectins Can Cause Leaky Gut

The gut wall becomes damaged when lectins attach to it.

The tiny hairs that line the mucosa become damaged and become less able to extract nutrients from food.

In a normal intestinal lining, the cells are tightly packed. They form what is referred to as “tight junctions.”

This prevents unwanted substances and molecules from leaking through the intestinal walls and entering the bloodstream (13).

These intestinal cells and their tight junctions are highly linked to immune processes (14).

When they are compromised, immune responses to antigens change.

As lectins enter the bloodstream through the now-permeable intestinal wall, they attach to glycoproteins on the outside of cells (15).

KEY POINT: Consistently consuming lectins can damage the lining of the intestines and create a leaky gut that allows unwanted substances into the bloodstream

Overexposure to Lectins Can Trigger Autoimmune Disease

red white blood cells

Lectins may also target antibodies, which help fight disease. In reaction, the immune system attacks the cells.

If the lectins are bound within the tissues of the body, the body may attack itself (16).

Wheat gliadin is a lectin that causes celiac disease (17).

It is often referred to as the “celiac disease toxin” (18).

People who are sensitive to this lectin may have a deficiency in certain peptides and a deficiency in their immune systems.

The autoimmune disease diabetes mellitus is linked to the lectin found in tomatoes.

Researchers have found connections between lectins and rheumatoid arthritis as well (19).

KEY POINT: Although autoimmune diseases are connected to deficiencies somewhere in the immune system, some researchers believe that they are caused or exacerbated by certain lectins.

You Can Remove Lectins by Cooking Your Food

metal bowl of green beans

Followers of the Paleo diet typically don’t eat legumes because they contain lectins.

Although proper preparation methods can reduce or eliminate lectins in certain foods, if you don’t know how the food was cooked, you may want to avoid it.

However, legumes contain carbohydrates, fiber and protein, and they can be very nutritious.

Research shows that simply soaking and boiling legumes for adequate amounts of time can remove virtually all of the lectins (20, 21).

If you don’t soak your beans long enough, you may not be able to encourage the heat to penetrate deeply enough to destroy all of the toxins.

You can’t just bake beans under dry heat, either. Research shows that dry heat doesn’t inactivate the lectins like boiling does (22).

In addition, low temperatures can actually increase lectin activity. This is why a slow cooker may not be the ideal vessel for cooking beans (23).

The amount of hemagglutinating units in raw red kidney beans is between 20,000 and 70,000 hau.

After cooking them properly, red kidney beans only contain about 200 to 400 hau.

Some research has shown that soybeans only need to be boiled for 5 to 10 minutes to eliminate almost all lectin activity (24).

KEY POINT: Properly soaking and boiling beans can remove almost all of the lectins, allowing you to eat them safely.

Soak, Sprout and Ferment Legumes to Make Them Safer

open green peas

Both lectins and phytates get in the way of your body’s absorption of nutrients (25, 26).

Although boiling under significant heat can reduce lectins in food, you can reduce the lectin activity without heat treatment.

Soaking seeds and grains before allowing them to germinate, or sprout, can help reduce lectins and phytates.

However, be careful when you sprout legumes.

Sprouting certain types of seeds or legumes, like lentils and alfalfa, can actually increase their lectin activity.

If you ferment seeds and grains, you are essentially allowing beneficial bacteria to eat the lectins.

This can reduce lectin activity in foods, making them easier on the digestive system (27, 28, 29).

Although nowadays most grains are processed in food manufacturing facilities, grains were traditionally fermented before consumption.

KEY POINT: You can soak, sprout or ferment grains to reduce their lectin activity.

Although you may soak and sprout legumes, you should still boil them before eating.

​Lectins in Canned Legumes

Usually canned legumes go through these stages:  cleaning, hydration,  electronic or manual classification post hydration, blanching, packaging, addition of sauce or brine, seaming of the cans, thermal processing, freezing, and labeling (30).

What we are concerned about is the blanching, and the thermal processing as these can deactivate the lectins.

table of canned legume processing stages for destroying lectins

Typically the heating treatment (in hot water) during the canning process is adequate to deactivate the lectins.

However, ​if you are unsure you can contact the manufacturer of canned legumes ​about their heating process.

KEY POINT: ​Canned legumes usually have their lectins destroyed during the heating treatment of the canning process.

Although lectins can be harmful and downright poisonous, they are not usually dangerous when consumed in the typical diet.

As long as you prepare lectin-rich foods properly, you shouldn’t experience any harmful effects.

If you have digestive issues or an autoimmune disease, you probably already know that your diet plays a large part in your condition.

You may see improvements in symptoms if you limit the amount of lectins in your diet.

However, foods that contain lectins have a lot of other beneficial nutrients, so you should make sure that you eat a variety of fresh, colorful and well-rounded foods.

If you would like to learn more about lectins, you can read Dr Gundry's Plant Paradox and his 100 lectin free recipes.

What do you think of dietary lectins? Share your thoughts below in the comments.

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  • Updated August 27, 2018

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Mary Ann

Hello and thank you so much for your research and for the article. There’s so much great information! Just a clarification needed please. On the Infographic in the Low Lectin section, even though you list fruits such as apples, nectarines and strawberries here as “low lectins”, there’s a comment to the right of the list that says “limit these fruits”. Can you please explain why? Thanks.

Phyllis

This is so helpful, especially the Infographic. Due to antibody testing, I have been on a restricted diet for a year and a half of no gluten, corn, dairy, peanuts, meat (except seafood), and green beans. But I was still getting sicker so was referred to a functional medicine practice. Understanding finally what is at the heart of my sypmtoms (Lupus) they want me off all Lectins. This just seemed overwhelming – especially the week of Thanksgiving. But after reading this site, I realize that I had only cleared part of the Lectins, so it was not the green bean… Read more »

Coralie

There is a new research done by Dr Gundry on lectins and a lot of helpful advice. We are following his protocol now due to my husband having bowel cancer!
He says dried beans are ok if pressure cooked, so I am glad about the information on canned beans.

Colleen

Hi Phyllis, also check out gundrymd.com dr gundry has decades of research on lectins and also excellent supplements to greatly reduce and repair their damage.

Penny Williamson

The problem vegetables listed: tomatoes, squash, eggplant, cucumbers, peppers, corn, peas, beans…are all staples of the Southern US diet. I assume canned tomatoes are ok, we eat a lot of fresh tomatoes, cucumbers, peppers (salad). What can be done about that? Does the amount of vinegar effective to deactivate lectins in these foods? Eggplant and squash are typically stir-fried or baked… what about eggplant parmesan typically baked in a tomato based sauce? The peas and beans are normally boiled in water, so no worries there. Can you comment on this? Thanks, PW from Birmingham, AL.

Billie

Yes please… these are all k my favorite foods. Can you please tell me how I can cook them to still be able to eat them PLEASE!!!!

Vanessa Ramos

Doesn’t strawberries also contain polyphenols Which is good for you? Im just trying to understand the balance.. I know there are foods that contain lectans but some of those same foods also contain polyphenol… So the objective is to find a happy medium.. Because there is no way to completely cut one out without the other. I just want tho understand the system so that i could plan accordingly.. This is very interesting..

Gabriel Castillo

Good evening I am Mexican and we have a Traditional way of making beans boil them but we also consume the broth. Is the broth now dangerous because of the lectins? Sometimes we also refry thembefode eating. And we use peruvian bean insted of Pinto can I get your feed back on this

Doug

Are you familiar with Dr. Steven Gundry’s Vital Reds? He seems to suggest we ought to eliminate lectins. That’s sure is a huge hit to what I really enjoy in the realm of food. Eliminate Tomato, Potato, Perppers? No more pizza and spaghetti??? Ugh.

Coralie

I guess it depends on how healthy you want your gut to be! It is best to eat fruit only in season and tomatoes capsicums etc are better as is most fruit when it is peeled and seeded, as that is where the lectins are concentrated!
Dr. Gundry explains that fruit is anything with skin and seeds, eg pumpkin, zucchini, breadfruit, cucumber etc. just peel and deseed. The Italians have been doing this for 100s of years when they make their traditional tomato spaghetti sauce and paste.

Mary
DanDaley

Wheat is problematic, and not just for people who test as gluten sensitive. Check out the books Wheat Belly by Davis, Grain Brain by Perlmutter, or The End of Alzheimer’s by Bredesen, and you will see that gluten and WGA (wheat germ agglutinin) are not your friends. I used to grind my own wheat and make all kinds of bread products, so I loved wheat, but I gave it up. I feel better and lost weight easily. Gundry is not perfect, as he does sometimes overstate his case -and he is too much a salesman, but he is generally on… Read more »

Jacqui

Mary, I am so glad you have given this link to people. I hope everyone will listen to Dr. Michael Greger on what he has to say. Please note that Gundry is making and will be making a large fortune because of his book. I found out about his book and his thesis yesterday and thought…no, this can’t be…so I proceeded to check it out. Please don’t be fooled, people. You will be putting yourself at risk for heart disease and who knows what else.

Melodie Rose

Doug, yes it’s hard. Health is wealth. Seems like a cliche, but it’s not.
What I want to be know: is lectins like gluten in that 0 should be eaten, or is it the amount of lectins in the blood is to high?
I hope that makes sense.

Sue Mitchel

What about canned beans?

Cheryl Perry

T Y so much for your research and information! I find it truly helpful. I am for most of my life on a gluten free diet. This has kept me slender and mostly healthy. 1 am 72 and for past 2 years, I have had more stomach distress, so starting researching possible causes. I discovered about lectins and will incorporate this new info into my life and diet.

Monica

What about canned legumes? Do they go through a special fermenting/soaking process to deactivate lectins? Or do we have to boil them again?

Aaron Peterson

I use a lot of peanut butter on my toast… it’s a daily thing I do. I try to buy coconut milk, for my Cheerios. Again daily. I usually have a pasta dish or a rice dish, both come to a boil, so that’s good? I also make lots of veggie chilli, with beans, and tomatoes and all those might shade veggies, but it boils. Usually when I make my food, I don’t get a leaky gut or diarrhea or stomach upset, but when I go out to eat or someone else prepares I do get a leaky gut. I’m… Read more »

Lee

I am wondering if Lectins are bad for Everyone? I eat peanut butter and bananas, oatmeal, and other foods that contain lectins but I never have any digestive issues??

Frankie Reed

For how long should I boil beans such as pintos to deactivate the lectins…I have been gf for 2 months and seen dramatic improvements with my fibro, brain fog, chronic fatigue, muscle spasms, and sleep both quality and quantity, but at 57 I am still searching for answers to restore the health of my youth that was quite extraordinary. Also, are digestive enzymes such as bromelain, pappain,and HCL recommended and do any of these digest lectins?

Francisca exposito

That was awesome thank you

Renee Lancaster

Quinoa is not a grain. It is a seed. Please correct your gross error.

Carol

Can you tell me if hard boiling eggs removes the lectin or if butter from grass fed cows has lectin in it or if yogurt has it? Is it just fruits with seeds in them? And are gluten free products ok. I use almond flour and co In it flour a lot. Are they bad because they are made from nuts.

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