What is Lectin?

Leucoagglutinin, a toxic phytohemagglutinin found in raw Vicia faba (fava bean).

The name “lectin” is derived from the Latin word legere, meaning, among other things, “to select”.

Long before a deeper understanding of their numerous biological functions, the plant lectins, also known as phytohemagglutinins, were noted for their particular high specificity for foreign glycoconjugates (e.g. those of fungi, invertebrates, and animals) and used in biomedicine for blood cell testing and in biochemistry for fractionation.

Is Lectin the New Gluten?

In recent research by Dr. Gundry and several other doctors they found that Gluten intolerance only affects 1% of the population. So, what’s causing all this inflammation and weight gain if it’s not gluten? Lectin.

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
  • peanuts
  • dairy products
  • nuts and seeds
  • garlic
  • marjoram
  • allspice

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.

What are Lectins?

Lectins are a type of protein that, in humans, may help cells interact with one another. Some scientists also believe that lectins provide a form of defense in plants to keep insects away.

Lectins are the natural insecticide and fungicide that plants produce to protect themselves from their environment. If an insect eats a tomato or eggplant, it dies from Lectin poisoning. So, what does this poison do to us?

These proteins also contain nitrogen, which is needed for plants to grow. While many parts of plants contain lectins, the seed is the part that people eat most often. Lectins may impact health in multiple ways, ranging from digestion to chronic disease risk. They have been shown to cause red blood cells to cluster together. They are categorized as antinutrients since they block the absorption of some nutrients.

Lectins are carbohydrate-binding proteins, macromolecules that are highly specific for sugar moieties. Lectins perform recognition on the cellular and molecular level and play numerous roles in biological recognition phenomena involving cells, carbohydrates, and proteins. Lectins also mediate attachment and binding of bacteria and viruses to their intended targets.

Lectins are ubiquitous in nature and are found in many foods. Some foods such as beans and grains need to be cooked or fermented to reduce lectin content, but the lectins consumed in a typical balanced diet are not harmful. Some lectins are beneficial, such as CLEC11A which promotes bone growth, while others may be powerful toxins such as ricin.

Lectins: The Diet Connection

A chemical reaction occurs between your blood and the foods you eat. This reaction is part of your genetic inheritance. It is amazing but true that today, in the twenty first century, your immune and digestive systems still maintain favoritism for foods that your blood type ancestors ate.

So, too, with the lectins in food. Simply put, when you eat a food containing protein lectins that are incompatible with your blood type antigen, the lectins target an organ or bodily system (kidneys, liver, gut, stomach, etc.) and can begin to interact with the tissues in that area.

Let’s say a Type A person eats a plate of lima beans. The lima beans are digested in the stomach through the process of acid hydrolysis. However, the lectin protein is resistant to acid hydrolysis. It doesn’t get digested, but it stays intact. It may interact directly with the lining of the stomach or intestinal tract, or it may get absorbed into your blood stream along with the digested lima bean nutrients. Different lectins target different organs and body systems.

Once the intact lectin protein settles someplace in your body, it literally has a magnetic effect on the cells in that region. It clumps the cells together and they are targeted for destruction, as if they, too, were foreign invaders. This clumping can cause irritable bowel syndrome in the intestines or cirrhosis in the liver or block the flow of blood through the kidneys – to name just a few of the effects. Lectins can also act as ‘fake hormones,’ latching onto the receptor for a hormone and either blocking the normal action of the hormone (this is called an ‘antagonist’) or revving up the hormone receptor non-stop (termed an ‘agonist.’)

Signs that you might be experiencing problems from lectins in your diet:

  • Bloating and flatulence after meals
  • Changes in bowel habits
  • Achy joints and muscles
  • Hormonal fluctuations
  • Skin eruptions
  • Fatigue and tiredness

Common Foods to Avoid For Each Blood Type That Contain Harmful Lectins 

Type O Type A Type B Type AB
·         Wheat

·         Soybean oil

·         Peanut

·         Kidney bean

·         Lima bean

·         Tomato

·         Eggplant

·         Garbanzo bean

·         Chicken

·         Corn

·         Soy

·         Lentil

·         Chicken

·         Corn

·         Banana

·         Fava bean


What do lectins do to the body?

  • 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. 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.
  • Lectins can enhance pancreas growth and increase the release of digestive enzymes.
  • 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.
  • 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.

Too Much Dietary Lectins Can Cause Leaky Gut

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

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.

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

Overexposure to Lectins Can Trigger Autoimmune Disease

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

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. Wheat gliadin is a lectin that causes celiac disease. It is often referred to as the “celiac disease toxin”.

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.

How to reduce Lectins in your diet

Lectins may be disabled by specific mono- and oligosaccharides, which bind to ingested lectins from grains, legume, nightshade plants (tomato, eggplant, potato) and dairy; binding can prevent their attachment to the carbohydrates within the cell membrane. The selectivity of lectins means that they are very useful for analyzing blood type, and they are also used in some genetically engineered crops to transfer traits, such as resistance to pests and resistance to herbicides.

Ways to decrease lectins in foods include:

  • boiling
  • fermentation
  • sprouting
  • peeling
  • deseeding
  • pressure cooking

While lectins have some undesirable effects, they also have some positive ones. Small amounts of lectins may help the good bacteria that live in human digestive systems.

What is the lectin-free diet?

Dr. Steven Gundry popularized the lectin-free diet. He is a former heart surgeon who switched his focus to food and supplement-based medicine. Dr. Gundry describes lectins as the main danger found in the American diet. In response, he has written a book that provides information on how to avoid lectins, alternative food choices, and recipes.

Possible benefits of the lectin-free diet

Following a lectin-free diet could be a way to lower inflammation in the body.

Some scientists believe lectins are harmful and cause inflammation. An older article links them to autoimmune diseases, including celiac disease, diabetes, and rheumatoid arthritis. One article discusses the research associated with wheat germ lectin. It may impact the immune system by increasing inflammation. Long-term inflammation is linked to many serious medical conditions, including heart disease, cancer, and depression.


Beans & Legumes – Beans carry more lectins than any other food. Do your best to limit beans, peas, lentils, and other legumes or cook them in a pressure cooker. Also, some legumes hide as nuts – so it’s best to cut out peanuts and cashews as well.

Grains – For the most part, grains are a relatively new food to us. Our hunter-gatherer ancestors didn’t search for grains. Plus, most grains are lectin bombs, as well as gluten-free grain substitutes. It’s best to limit grain intake. If you must, eat white flour over wheat.

Squash – An easy rule to remember is that any vegetable with seeds is actually considered a fruit. Such is the case with squash, pumpkins, and zucchini. The seeds and peels of these foods are full of lectins. If you MUST eat squash, make sure to toss the peels and seeds aside.

Nightshades – Nightshades are vegetables that include eggplant, any kind of pepper, potatoes, and tomatoes. The peels and the seeds of these plants contain loads of lectins, too. Make sure to peel and deseed them or pressure cook or ferment them. All these techniques reduce the amount of lectins.

In-Season Fruit – Again, it’s nature’s candy, so you’ll want to limit the quantity you eat, but when it’s in season, fruit is okay to add to your diet.


Corn and corn-fed ‘free-range’ meats – It doesn’t take much to see why corn is among the worst lectin-filled grains. Just look at the American farm industry. Farmers use corn for the sole purpose of fattening up cattle. And, guess what? Corn has the same effect on us. Not only that, it causes fatty deposits in the muscle. So, avoid ‘free-range’ meats. ‘Free-range’ means the cattle are eating corn and, therefore, so are you. Instead, opt for only pasture-raised meats.

Casein A1 Milk – It may sound like science fiction, but a couple thousand years ago cows in Northern Europe suffered a genetic mutation. The result was a lectin-like protein in their milk called casein A1. Turns out, casein A1 is converted to a protein called beta-casomorphin. And this protein can prompt an immune attack on the pancreas of people who consume milk from these cows, or cheeses made from it.

Most store-bought milk in your grocery store, even if it’s organic, is A1 milk. The unmutated cows, found primarily in Southern Europe, produce a safe protein called casein A2. When people think they’re lactose intolerant, they’re generally affected by casein A1. So, eliminate casein A1 milk from your diet.

Instead, stick to A2 milk, Southern European cow’s milk, goat’s milk, and buffalo milk. Health foods stores are pretty good about carrying these. Also, consider these milks an indulgence, and consume them only in moderate quantities.


Cooked tubers – Sweet potatoes, yucca, and taro root are a great source of vitamins and minerals. That’s because their roots have strong absorption abilities and draw water and minerals from the soil for nourishment also, they’re also high in fiber that feeds your good gut bugs.

Leafy Greens – Romaine, red & green leaf lettuce, kohlrabi, mesclun, spinach, endive, butter lettuce, parsley, fennel, and seaweed/sea vegetables are all great to add to a lectin-free diet. They are high in nutrients and incredible for your health. To boot, they are very filling, especially if you drizzle olive or avocado oil on them!

Cruciferous & other great vegetables – Load up on broccoli, cauliflower, and Brussels sprouts. And include these lectin-free veggies in your diet as often as you like: asparagus, garlic, celery, mushrooms, and onion. They are full of fiber and polyphenols.

Avocado – Now, avocado is a fruit, but it’s actually okay to eat when ripe because it’s essentially sugar-free! Not to mention, it’s full of good fat and soluble fiber – key when trying to lose weight and absorb antioxidants.

Olives and Extra Virgin Olive Oil – Olive oil is filled with essential vitamins and minerals. For instance, it contains vitamin K, vitamin E, calcium, iron, sodium, and potassium. Furthermore, olive oil contains polyphenols and fatty acids. It’s an all-around superfood.

In fact, olive oil can contribute to the reduction of inflammatory activity in those suffering from autoimmune disorders.4 And, it’s an incredible source of polyphenols, especially oleuropein – a.k.a. the longevity polyphenol.


Use a pressure cooker – If you’re cooking with beans, tomatoes, potatoes, and quinoa, the pressure cooker is your best bet for destroying plant lectins. But, using a pressure cooker doesn’t get rid of all lectins – it won’t even touch the lectins in wheat, oats, rye, barley, or spelt.

Peel and Deseed your fruits and veggies – If you’re going to use lectin-rich plant foods, make sure to peel and deseed them. Often, the most harmful part of a plant is it’s lectin-filled hull, peel, or rind. To reiterate, the peels and the seeds are often where lectins are hiding, so you can significantly cut down on your intake by eliminating that part of the plant.

White over brown – Finally, if in fact you must eat grains, opt for white over brown. So, instead of brown rice, eat white rice. Instead of whole wheat bread, find a healthier version of white bread.

Turns out, though many believe brown rice is healthier than it’s white counterpart, those who eat rice as their staple grain have always stripped the hull off of brown rice before they eat it. That’s because the hull contains all the dangerous lectins.

Sprouting – Allowing seeds, grains, and beans to sprout can help reduce lectin content related to the process of germination. In general, the greater the sprouting duration, the lesser concentration of lectins.

Soaking and Cooking – Soaking raw beans and grains is suggested to minimize lectin content. As a general rule of thumb, soak beans for at least two hours, or overnight if possible. Adding baking soda and pressure-cooking can also lessen lectin concentration.

Fermenting – Fermentation is the process in which beneficial bacteria are able to reduce harmful substances in the body, and mostly known in sauerkraut, yogurt, tempeh, kombucha, and other fermented foods. The fermentation process has shown to reduce lectin content up to 95 percent.

Are Lectins In or Out?

To truly gauge whether or not lectin-supplying foods are blocking nutrients is difficult, as researchers do not have clear evidence regarding its effects on the body. However, most nutrition experts suggest consuming a well-balanced diet limits the risk of nutritional deficiencies. If interested in or following a specific diet, consulting with a dietitian is encouraged, especially if single or multiple food groups are restricted or eliminated. Their expertise and guidance can also help determine whether or not following a lectin-free diet is right for you.

Limit but Don’t Eliminate All Lectins (Mercola.com)

In summary, while I believe lectins have the potential to wreak havoc on health, complete avoidance is neither possible nor ideal. Conducting an online search for “lectin-rich foods” will yield lists that are so long, they basically encompass the entire vegetable kingdom. You cannot eliminate them all, and since SOME lectins have health benefits, you wouldn’t want to, either.

The key is to identify the worst culprits, cut those out, and make sure you prepare and cook certain high-lectin foods properly to make them safer to eat. Naturally, your individual situation will determine just how strict you need to be. Many people, especially those with autoimmune disorders, tend to be particularly sensitive to specific lectins found in specific foods.

So, experimentation may be needed to identify them. As a general rule, I recommend paying particular attention to lectins if you are currently eating a healthy, whole food diet yet continue to have health problems. While not a guarantee for success, eliminating or reducing lectins just might be the missing key to your healing.

Lectin use in medicine and medical research

Purified lectins are important in a clinical setting because they are used for blood typing. Some of the glycolipids and glycoproteins on an individual’s red blood cells can be identified by lectins.

  • A lectin from Dolichos biflorus is used to identify cells that belong to the A1 blood group.
  • A lectin from Ulex europaeus is used to identify the H blood group antigen.
  • A lectin from Vicia graminea is used to identify the N blood group antigen.
  • A lectin from Iberis amara is used to identify the M blood group antigen.
  • A lectin from coconut milk is used to identify Theros antigen.
  • A lectin from Carex is used to identify R antigen.

In neuroscience, the anterograde labeling method is used to trace the path of efferent axons with PHA-L, a lectin from the kidney bean. A lectin (BanLec) from bananas inhibits HIV-1 in vitro. Achylectins, isolated from Tachypleus tridentatus, show specific agglutinating activity against human A-type erythrocytes. Anti-B agglutinins such as anti-BCJ and anti-BLD separated from Charybdis japonica and Lymantria dispar, respectively, are of value both in routine blood grouping and research.

Use in studying carbohydrate recognition by proteins

Lectins from legume plants, such as PHA or concanavalin A, have been used widely as model systems to understand the molecular basis of how proteins recognize carbohydrates, because they are relatively easy to obtain and have a wide variety of sugar specificities. The many crystal structures of legume lectins have led to a detailed insight of the atomic interactions between carbohydrates and proteins.

Use as a biochemical tool

Concanavalin A and other commercially available lectins have been used widely in affinity chromatography for purifying glycoproteins. In general, proteins may be characterized with respect to glycoforms and carbohydrate structure by means of affinity chromatography, blotting, affinity electrophoresis, and affinity immunoelectrophoreis with lectins as well as in microarrays, as in evanescent-field fluorescence-assisted lectin microarray.

Use in biochemical warfare

One example of the powerful biological attributes of lectins is the biochemical warfare agent ricin. The protein ricin is isolated from seeds of the castor oil plant and comprises two protein domains. Abrin from the jequirity pea is similar:

  • One domain is a lectin that binds cell surface galactosyl residues and enables the protein to enter cells
  • The second domain is an N-glycosidase that cleaves nucleobases from ribosomal RNA, resulting in inhibition of protein synthesis and cell death.


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