About Lectins, Beans -- and why soak them?

assorted image of beans

What are lectins?

Lectins are glycoproteins of 60,000-100,000 MW. They are carbohydrate-binding proteins, macromolecules that are highly specific for sugar moieties and are known for their ability to agglutinate (clump) erythrocytes in vitro.

Lectins 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. The molecular properties of lectins offer a way for molecules to stick together which can influence cell-cell interaction much like the lock-and-key binding found with enzyme and substrate. Lectins are found in both plants and animals. Lectins found in plants are known to be toxic to animals.

Why do plants have toxic lectins ?

Plant lectins are toxic to all animals so basically these so called -Anit-nutrients- Gluten, Lectins and Phytates—are plants’ way of protecting themselves against being eaten.

Structure of Lectins

Shown below is the structure of the most common animal lectin. The upper left shows how protein presents a tight fit with the sugar galactose.


human galectin bound to galactose


Lectins in Food

Foods with high concentrations of lectins, consist of: beans, cereal grains, seeds, nuts, and potatoes. If consumed in excess, they may be harmful when uncooked or improperly-cooked. Adverse effects may include nutritional deficiencies, and immune (allergic) reactions. Most effects of lectins are due to gastrointestinal distress through interaction of the lectins with the epithelial cells of the gut by binding. 

How do plant lectins cause intestinal distress

Plant Lectins cannot be fully digested by humans and can they enter the bloodstream. Our immune system then recognizes them as foreign, attacks them causing an inflammatory response. Because fo their affinity to sugar moeties, lectins can bind to our intestinal lining. There they can damage our intestines in a way that creates openings large enough to allow large undigested proteins to enter our bloodstream. This sets off and immune response against these unfamiliar invaders, which causes the body to have a systemic inflammatory response. Beans have a very high concentration of lectins. So much that just five raw Kidney Beans can kill a human. This will happen because the lectins will bind to the sugar molecules on the surface of our red blood cells and cause them to clump together and coagulate the blood. But food poisoning contracted from raw or undercooked beans is completely preventable by properly cooking them.

Lectins and Autoimmune Disease

"..In diet responsive rheumatoid arthritis one of the commonest trigger foods is wheat, and wheat lectin is specific for N-acetyl glucosamine—the sugar that is normally hidden but exposed in rheumatoid arthritis. This suggests that N-acetyl glucosamine oligomers such as chitotetraose (derived from the chitin that forms crustacean shells) might be an effective treatment for diet associated rheumatoid arthritis. Interestingly, the health food trade has already siezed on N-acetyl glucosamine as an antiarthritic supplement..." (see Reference 3)

How to prevent lectin toxicity?

Grains, beans, nuts, and seeds in their natural form were never consumed in ancient times without being soaked or fermented first. Soaking releases some of the lectins which can be drained off. Adding baking soda or vinegar increases the Perhaps one of the safest methods of cooking beans is in a pressure cooker where the temperatures are much higher. Pressure cooking seems to be particularly effective at inactivating lectins.

Supplements and Diet 

Foods such as seaweeds and ground up shrimp shells bind Lectins. Also MSM or Glucosaminetablets used by many for joints works against lectins. The most effective form of glucosamine for binding lectin from wheat is N-Acetyl-D-glucosamine. Below is shown the crystal structure of the lectin, wheat germ aglutinin, bound to glucosamine. When glucosamine is bound to lectins is prevents binding to cell surface sugar moeities.


human galectin bound to galactose


What is a Paleo Style Diet?



1-Why must you soak beans before cooking them

2-Structural Basis of Multivalent Binding to Wheat Germ Agglutinin

3-Do dietary lectins cause disease?- The evidence is suggestive—and raises interesting possibilities for treatment 

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