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. Some lectins are beneficial, such as CLEC11A which promotes bone growth or the Antigen Binding Lectins in certain mushrooms, while others may be powerful toxins such as ricin.
Lectins may be disabled by specific mono- and oligosaccharides, which bind to ingested lectins from grains, legume, nightshadeplants and dairy; binding can prevent their attachment to the carbohydrates within the cell membrane. The selectivity of lectins means that they are 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. W.C. Boyd introduced term ‘lectin’ in 1954 from Latin word ‘choose’.
Types of Plant Lectins
In plants, lectins are concentrated in seeds, early stage leaves, and roots. Leaves typically contain fewer lectins, although this may vary from plant to plant. A great example of a leaf is romaine lettuce.
The types of lectins that are often found in foods and can produce sensitivity include [R, R]: Legume lectins, such as white kidney beans. On average, 15% percent of a bean’s proteins are lectins. Cucurbitaceae lectins, found in the sap or juice of cucumber, melon, and squash. Prolamins, such as gluten and gliadin, are the alcohol-soluble lectins found in cereal grains. Agglutinin or hemagglutinin is so-called as it can cause blood agglutination (clumping of blood cells). Examples include wheat germ and soybean agglutinins [R].
Plant agglutinins have been characterized by testing their ability to clump blood cells of certain blood types, which suggests that people with certain blood types may be more susceptible to health problems due to lectins than others [R]. Some plant lectins, such as castor bean ricin and white kidney bean agglutinins, are very toxic to humans and rats. Ricin can cause blood agglutination and might be used in chemical warfare and genetically engineered herbicides. White kidney bean hemagglutinins can cause acute nausea, followed by vomiting and diarrhea. (Source)
Lectins serve many different biological functions in animals, from the regulation of cell adhesion to glycoprotein synthesis and the control of protein levels in the blood. They also may bind soluble extracellular and intercellular glycoproteins. Some lectins are found on the surface of mammalian liver cells that specifically recognize galactose residues. It is believed that these cell-surface receptors are responsible for the removal of certain glycoproteins from the circulatory system.
Another lectin is a receptor that recognizes hydrolytic enzymes containing mannose-6-phosphate, and targets these proteins for delivery to the lysosomes. I-cell disease is one type of defect in this particular system.
Lectins also are known to play important roles in the immune system. Within the innate immune system lectins such as the MBL, the mannose-binding lectin, help mediate the first-line defense against invading microorganisms. Other lectins within the immune system are thought to play a role in self-nonself discrimination and they likely modulate inflammatory and autoreactive processes. Intelectins (X-type lectins) were shown to bind microbial glycans and may function in the innate immune system as well. Lectins may be involved in pattern recognition and pathogen elimination in the innate immunity of vertebrates including fishes.
The function of lectins in plants (legume lectin) is still uncertain. Once thought to be necessary for rhizobia binding, this proposed function was ruled out through lectin-knockout transgene studies.
The large concentration of lectins in plant seeds decreases with growth, and suggests a role in plant germination and perhaps in the seed’s survival itself. The binding of glycoproteins on the surface of parasitic cells also is believed to be a function. Several plant lectins have been found to recognize non-carbohydrate ligands that are primarily hydrophobic in nature, including adenine, auxins, cytokinin, and indole acetic acid, as well as water-soluble porphyrins. It has been suggested that these interactions may be physiologically relevant, since some of these molecules function as phytohormones.
It is hypothesized that some hepatitis C viral glycoproteins attach to C-type lectins on the host cell surface (liver cells) to initiate infection. To avoid clearance from the body by the innate immune system, pathogens (e.g., virus particles and bacteria that infect human cells) often express surface lectins known as adhesins and hemagglutinins that bind to tissue-specific glycans on host cell-surface glycoproteins and glycolipids.
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.L
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.
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.
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.
Are Lectins really harmful for humans ?
Many legume seeds have been proven to contain high lectin activity, termed “hemagglutination.” Soybean is the most important grain legume crop in this category. Its seeds contain high activity of soybean lectins (soybean agglutinin or SBA). SBA is able to disrupt small intestinal metabolism and damage small intestinal villi via the ability of lectins to bind with brush border surfaces in the distal part of small intestine. There can be adverse effects that include nutritional deficiencies, and immune (allergic) reactions when certain foods are eaten raw.. However, when they are sprouted. soaked or cooked, these deleterious effects go away. However, this fact did not stop the food fad marketers from creating a new “Anti-Lectin” Diet.
The Anti-Lectin Diet
This Diet is based on the following: meat and seafood ad libidum (in abundance) and no grains, beans, nuts, seeds, potatoes, nite shades and all dairy. Allowed foods include all seafood, meat, chicken/turkey (all fowl), eggs, and most fruits and vegetables. Romaine lettuce, cruciferous veggies, cucumbers, and celery would be the best vegetables to include. Raw honey, citrus fruits, berries, and pineapple are the recommended fructose-containing foods.
Even cooking, it is argued, may not be enough. Lectins may get removed, but anti-nutrients would still exist. For example, tannins are found in many plants and are considered anti-nutritional because they can alter nutrient digestion and absorption (Source)
However, red wines also have an abundance of tannins and it is these tannins that synergistically boosts red wine’s health and longevity punch. So we must read these studies with critical eyes.
For the Anti Lectin School, the evidence of harm is as follows:
Lectins can withstand heat and digestion in both rats and humans. Plant lectins have also been recovered intact in human feces [R, R]. They can be readily transported through the gut wall into the blood [R]. In the blood, lectins may stimulate the immune system and modify hormone functions, or get deposited in blood and lymphatic walls [R, R]. Lectins bind to surface glycoproteins and gut lining cells, causing damage to the villi, increasing the uptake of intestinal content by the cells, and shortening the microvilli [R]. Some dietary sources of lectins, such as wheat, can directly break tight junctions in gut cells [R]. Lectins cause leaky gut, allowing increased exposure of both dietary and bacterial antigens (inflammatory agents) to the immune system [R]. Lectins can also interfere with nutrient absorption [R].
Furthemore, as lectins cause leaky gut and are readily absorbed into the bloodstream, most people develop antibodies against dietary lectins [R, R]. These antibodies don’t necessarily protect you from harmful lectins. Whether this causes disease depends on individual susceptibility. In mice, administration of lectins through the nose or by feeding stimulates IgG and IgA production, similar to that of the cholera toxin [R].
Lectins can potentiate the immune response to antigens that wouldn’t be inflammatory by themselves. For example, mice fed with wheat germ agglutinin and egg white protein develop much stronger antibody responses to egg white protein than if they are fed egg white protein alone [R, R].Therefore, consumption of lectin-containing foods concomitantly with other products can increase the likelihood of developing sensitivity to other food products.
In addition, As lectins can act as triggers to the immune system and leaky gut, lectins can cause autoimmunity in susceptible people [R]. Lectins are said to trigger autoimmunity by binding to glycoproteins and glycolipids (sugar molecules attached to proteins and fat), such as sialic acid, on the surface of the cells. Interestingly, the brain and gut are rich in sialic acid.
In humans, sialic acid is present in body fluids (blood, breast milk, gallbladder excretions, synovial fluid, sweat, gastric juices, and urine) and tissues (red and white blood cells, platelets, salivary glands, throat, stomach, cervix, colon, cartilage, etc.). In the blood, it’s found in fibrinogen, haptoglobin, ceruloplasmin, α1 -antitrypsin, complement proteins, and transferrin [R].
Under certain conditions, lectins can increase inflammation by stimulating IFN-gamma, IL-1, and TNF-alpha production as well as HLA class II expression in gut cells [R]. The presence of lectins affects the composition of the gut bacteria and may cause dysbiosis (microbial imbalance) predisposing you to autoimmune diseases. However, the mechanism by which lectins affect gut bacteria is not fully understood.
Lectins reduce levels of intestinal heat shock protein (iHSPs), an anti-inflammatory protein that is important for healthy interaction with the gut bacteria. Also, lectins interfere with iHSP functions, thus reducing the gut lining’s sensitivity to oxidation and inflammation [R]. In rats, dietary lectins increase gut levels of E. coli and Lactobacillus lactis, both of which have proteins similar to HLA and are associated with autoimmune diseases such as rheumatoid arthritis [R]. Kidney bean lectins can cause E. coli overgrowth in the gut, while snowdrop lectins and mannose-specific lectins can block this effect [R]. Lectins can cause enlargement and overgrowth of cells in many tissues, including the intestine, pancreas, and liver [R, R]. In cell-based studies, lectins triggered lymphocyte growth and activation [R].
At low doses, wheat germ agglutinin can mimic the insulin function in fat cells. However, at higher doses, wheat germ agglutinin can cause insulin resistance (in a cell-based study) [R]. Enlargement of the pancreas due to dietary lectins may reduce insulin levels in rats [R]. In a cell-based study, wheat germ agglutinin and ricin from castor oil can increased fat synthesis in fat cells [R]. In roundworms, lectins can be transported from the gut to dopamine neurons, and interfere with neuronal and dopamine functions, suggesting that it may contribute to Parkinson’s disease in humans [R].
Can the Elimination of Lectin Reverse Autoimmune Disease ?
A study of 800 autoimmune patients evaluated a diet that avoided grains, sprouted grains, pseudo-grains, beans and legumes, soy, peanuts, cashews, nightshades, melons and squashes, non-Southern European cow milk products (Casein A1), and grain/bean-fed animals. Most of these patients started with elevated levels of TNF-alpha (an inflammatory molecule), which were reduced to normal after 6 months on this diet. The study concluded that increased adiponectin is a marker for lectin and gluten sensitivity, while TNF-alpha can be used as a marker for gluten/lectin exposure in sensitive individuals [R].Dr. Steven Gundry, the author of the study, has a financial interest with debunking all lectins.
The Happiness Institute has not had enough time to evaluate all of these above-mentioned claims.
The Science that supports this type of type is based on animal and lab studies, few clinical trials. Futhermore, many of these tests have been done with uncooked or unsprouted plants. It is acknowledged that Plants secrete their own “poisons” to ward off predators and that some of these molecules can be harmful to humans. But the whole pictures also shows that some of these molecules can be beneficial and when prepared holistically, these plant foods are beneficial. Furthermore, all of the longevity zone studies show that the centenarians who live the longest and the healthiest eat lots of lectin-based plant foods.
Lectins are ubiquitous in nature and many foods contain the proteins. Because some lectins can be harmful if poorly cooked or consumed in great quantities, “lectin-free” fad diets have been proposed, most based on the writing of Steven Gundry. A typical lectin-free diet excludes a range of foods, including most grains, pulses and legumes, as well as eggs, seafood and many staple fruits and vegetables. These foods do not contain harmful levels of lectins when properly cooked, and there is no health benefit to following these diets for most people. A strict lectin-free diet is unbalanced and dangerously low in many nutrients, requiring significant dietary supplementation to maintain health.
Lectins are one of many toxic constituents of many raw plants, which are inactivated by proper processing and preparation (e.g., cooking with heat, fermentation). For example, raw kidney beans naturally contain toxic levels of lectin (e.g. phytohaemagglutinin).
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.
Although they were first discovered more than 100 years ago in plants, now lectins are known to be present throughout nature. It is generally believed that the earliest description of a lectin was given by Peter Hermann Stillmark in his doctoral thesis presented in 1888 to the University of Dorpat. Stillmark isolated ricin, an extremely toxic hemagglutinin, from seeds of the castor plant (Ricinus communis).
The first lectin to be purified on a large scale and available on a commercial basis was concanavalin A, which is now the most-used lectin for characterization and purification of sugar-containing molecules and cellular structures. The legume lectins are probably the most well-studied lectins.
Most lectins do not possess enzymatic activity. may bind to a soluble carbohydrate or to a carbohydrate moiety that is a part of a glycoprotein or glycolipid. They typically agglutinate certain animal cells and/or precipitate glycoconjugates. Lectins are considered a major family of protein antinutrients (ANCs), which are specific sugar-binding proteins exhibiting reversible carbohydrate-binding activities.Lectins are similar to antibodies in their ability to agglutinate red blood cells.
TEXT UNDER CONSTRUCTION
|Table of the major plant lectins |
|Lectin Symbol||Lectin name||Source||ligand motif|
|Mannose binding lectins|
|ConA||Concanavalin A||Canavalia ensiformis||α-D-mannosyl and α-D-glucosyl residues
branched α-mannosidic structures (high α-mannose type, or hybrid type and biantennary complex type N-Glycans)
|LCH||Lentil lectin||Lens culinaris||Fucosylated core region of bi- and triantennary complex type N-Glycans|
|GNA||Snowdrop lectin||Galanthus nivalis||α 1-3 and α 1-6 linked high mannose structures|
|Galactose / N-acetylgalactosamine binding lectins|
|RCA||Ricin, Ricinus communis Agglutinin, RCA120||Ricinus communis||Galβ1-4GalNAcβ1-R|
|PNA||Peanut agglutinin||Arachis hypogaea||Galβ1-3GalNAcα1-Ser/Thr (T-Antigen)|
|AIL||Jacalin||Artocarpus integrifolia||(Sia)Galβ1-3GalNAcα1-Ser/Thr (T-Antigen)|
|VVL||Hairy vetch lectin||Vicia villosa||GalNAcα-Ser/Thr (Tn-Antigen)|
|N-acetylglucosamine binding lectins|
|WGA||Wheat Germ Agglutinin, WGA||Triticum vulgaris||GlcNAcβ1-4GlcNAcβ1-4GlcNAc, Neu5Ac (sialic acid)|
|N-acetylneuraminic acid binding lectins|
|SNA||Elderberry lectin||Sambucus nigra||Neu5Acα2-6Gal(NAc)-R|
|MAL||Maackia amurensis leukoagglutinin||Maackia amurensis||Neu5Ac/Gcα2,3Galβ1,4Glc(NAc)|
|MAH||Maackia amurensis hemoagglutinin||Maackia amurensis||Neu5Ac/Gcα2,3Galβ1,3(Neu5Acα2,6)GalNac|
|Fucose binding lectins|
|UEA||Ulex europaeus agglutinin||Ulex europaeus||Fucα1-2Gal-R|
|AAL||Aleuria aurantia lectin||Aleuria aurantia||Fucα1-2Galβ1-4(Fucα1-3/4)Galβ1-4GlcNAc,
- URS Rutishauser and Leo Sachs (May 1, 1975). “Cell-to-Cell Binding Induced by Different Lectins”. Journal of Cell Biology. Rockefeller University Press. 65 (2): 247–257. doi:10.1083/jcb.65.2.247. PMC 2109424. PMID 805150.
- Matthew Brudner, Marshall Karpel, Calli Lear, Li Chen, L. Michael Yantosca, Corinne Scully, Ashish Sarraju, Anna Sokolovska, M. Reza Zariffard, Damon P. Eisen, Bruce A. Mungall, Darrell N. Kotton, Amel Omari, I-Chueh Huang, Michael Farzan, Kazue Takahashi, Lynda Stuart, Gregory L. Stahl, Alan B. Ezekowitz, Gregory T. Spear, Gene G. Olinger, Emmett V. Schmidt, and Ian C. Michelow1 (April 2, 2013). Bradley S. Schneider, ed. “Lectin-Dependent Enhancement of Ebola Virus Infection via Soluble and Transmembrane C-type Lectin Receptors”. PLoS ONE. 8 (4 specific e code=e60838): e60838. Bibcode:2013PLoSO…860838B. doi:10.1371/journal.pone.0060838. PMC 3614905. PMID 23573288.
- Chan, Charles KF; Ransom, Ryan C; Longaker, Michael T (13 December 2016). “Lectins bring benefits to bones”. eLife. 5. doi:10.7554/eLife.22926. PMC 5154756. PMID 27960074.
- “THE LECTIN STORY”.
- “Lectin list” (PDF). Interchim. 2010. Retrieved 2010-05-05.
- Walker, R. (2007). “The use of lectins in histopathology”. Histopathology. 9 (10): 1121–1124. doi:10.1111/j.1365-2559.1985.tb02790.x.
- Els. J. M. Van Damme, Willy J. Peumans, llArpad Pusztai, Susan Bardocz (March 30, 1998). Handbook of Plant Lectins: Properties and Biomedical Applications. John Wiley & Sons. pp. 7–8. ISBN 978-0-471-96445-2. Retrieved 18 April 2013.
- Maverakis E, Kim K, Shimoda M, Gershwin M, Patel F, Wilken R, Raychaudhuri S, Ruhaak LR, Lebrilla CB (2015). “Glycans in the immune system and The Altered Glycan Theory of Autoimmunity”. J Autoimmun. 57 (6): 1–13. doi:10.1016/j.jaut.2014.12.002. PMC 4340844. PMID 25578468.
- Arasu, Abirami; Kumaresan, Venkatesh; Sathyamoorthi, Akila; Palanisamy, Rajesh; Prabha, Nagaram; Bhatt, Prasanth; Roy, Arpita; Thirumalai, Muthukumaresan Kuppusamy; Gnanam, Annie J.; Pasupuleti, Mukesh; Marimuthu, Kasi; Arockiaraj, Jesu (2013). “Fish lily type lectin-1 contains β-prism architecture: Immunological characterization”. Molecular Immunology. 56 (4): 497–506. doi:10.1016/j.molimm.2013.06.020. PMID 23911406.
- Oldroyd, Giles E.D.; Downie, J. Allan (2008). “Coordinating Nodule Morphogenesis with Rhizobial Infection in Legumes”. Annual Review of Plant Biology. 59: 519–46. doi:10.1146/annurev.arplant.59.032607.092839. PMID 18444906.
- Komath SS, Kavitha M, Swamy MJ (March 2006). “Beyond carbohydrate binding: new directions in plant lectin research”. Org. Biomol. Chem. 4 (6): 973–88. doi:10.1039/b515446d. PMID 16525538.
- R. Bartenschlager, S. Sparacio (2007). “Hepatitis C Virus Molecular Clones and Their Replication Capacity in Vivo and in Cell Culture”. Virus Research. Elsevier. 127 (2): 195–207. doi:10.1016/j.virusres.2007.02.022. PMID 17428568.
- Soto, GE; Hultgren, SJ (1999). “Bacterial adhesins: common themes and variations in architecture and assembly”. J Bacteriol. 181 (4): 1059–1071. PMID 9973330.
- Sharon, N.; Lis, H (2004). “History of lectins: From hemagglutinins to biological recognition molecules”. Glycobiology. 14 (11): 53R–62R. doi:10.1093/glycob/cwh122. PMID 15229195.
- Carlson, Neil R. (2007). Physiology of behavior. Boston: Pearson Allyn & Bacon. ISBN 0-205-46724-5.
- Swanson, M. D.; Winter, H. C.; Goldstein, I. J.; Markovitz, D. M. (2010). “A Lectin Isolated from Bananas is a Potent Inhibitor of HIV Replication”. Journal of Biological Chemistry. 285 (12): 8646–55. doi:10.1074/jbc.M109.034926. PMC 2838287. PMID 20080975.
- Viswambari Devi, R.; Basilrose, M. R.; Mercy, P. D. (2010). “Prospect for lectins in arthropods”. Italian Journal of Zoology. 77 (3): 254–260. doi:10.1080/11250003.2010.492794.
- “Immobilized Lectin”. legacy.gelifesciences.com.
- Glyco Station, Lec Chip, Glycan profiling technology Archived 2010-02-23 at the Wayback Machine
- Rosenbloom, Cara (7 July 2017). “Going ‘lectin-free’ is the latest pseudoscience diet fad”. Washington Post. Retrieved 28 July 2017.
- Warner, Anthony (27 July 2017). “Lectin-free is the new food fad that deserves to be skewered”. New Scientist. Retrieved 28 July 2017.
- Taylor, Steve (2008). “40: Food Toxicology (Lectins: Cell-Agglutinating and Sugar-Specific Proteins)”. In Metcalfe, Dean; Sampson, Hugh; Simon, Ronald. Food Allergy: Adverse Reactions to Foods and Food Additives (4th ed.). pp. 498–507.
- Cordain, Loren; Toohey, L.; Smith, M. J.; Hickey, M. S. (2007). “Modulation of immune function by dietary lectins in rheumatoid arthritis”. British Journal of Nutrition. 83 (3): 207–17. doi:10.1017/S0007114500000271. PMID 10884708.
- Goldstein, Erwin; Hayes, Colleen (1978). “The Lectins: Carbohydrate-Binding Proteins of Plants and Animals”. Advances in Carbohydrate Chemistry and Biochemistry. Advances in Carbohydrate Chemistry and Biochemistry. 35: 127–340. doi:10.1016/S0065-2318(08)60220-6. ISBN 9780120072354. PMID 356549.
- Sharon, Nathan; Lis, Halina (1972). “Lectins: Cell-Agglutinating and Sugar-Specific Proteins”. Science. 177 (4053): 949–959. Bibcode:1972Sci…177..949S. doi:10.1126/science.177.4053.949.
- Ellen, R.P.; Fillery, E.D.; Chan, K.H.; Grove, D.A. (1980). “Sialidase-Enhanced Lectin-Like Mechanism for Actinomyces viscosus and Actinomyces naeslundii Hemagglutination”. Infection and Immunity. 27 (2): 335–343.
- Hajos, Gyongyi; Gelencser, Eva (1995). “Biological Effects and Survival of Trypsin Inhibitors and the Agglutinin from Soybean in the Small Intestine of the Rat”. Journal of Agricultural and Food Chemistry. 43 (1): 165–170. doi:10.1021/jf00049a030.