What are Lectins?

Written By Dr. Wayne Sodano,
Director of Clinical Support & Education For Evexia Diagnostics

Lectins are carbohydrate-binding proteins present in most plants, especially seeds like cereals, beans, etc., in tubers like potatoes, and also in animals. Dietary lectins act as protein antigens, which bind to surface glycoproteins (or glycolipids) on erythrocytes or lymphocytes.”¹ “Plant lectins, otherwise known as phyto-hemagglutinins or hemagglutinins, have been shown to possess a remarkable array of biological activities. In vitro, lectins have been shown to effect lymphocyte mitogenesis (both stimulating and inhibiting with the lymphocytes of the gastrointestinal tract being most susceptible), to possess the ability to aggregate immunoglobulins, to trigger the alternate complement pathway, to inhibit fungal growth, and to induce histamine release.”²

“Lectins can bind to carbohydrates on various cells. Many of the receptors are membrane-integrated glycoproteins and function as receptors for hormones and cytokines, or are involved in cell-cell recognition. By binding to these receptors, lectins may mimic a natural ligand of the receptors or inhibit binding of a natural ligand and thereby evoke a variety of systemic and local effects.”³ “In addition, lectins that are transported across the gut wall into systemic circulation can modulate the body’s hormone balance, metabolism, and health.

In contrast to dietary proteins, lectins resist degradation in the small intestine and are also resistant to breakdown by most gut bacteria. Thus, most lectins survive, at least in part, the passage through the digestive tract in an immunologically and functionally intact form.”⁴ The ‘eating right for your blood type’ theory is based on the reaction of certain lectins with a specific blood type. This theory has been the subject of much criticism; however there seems to be a correlation between diet and blood type as a chemical reaction occurs between the blood and the foods that one eats, and this reaction is part of genetic inheritance.⁵

“Lectins have potent in vivo effects. When consumed in excess by sensitive individuals, they can cause severe intestinal damage disrupting digestion and causing nutrient deficiencies. They can provoke IgG and IgM antibodies causing food allergies and other immune responses, and they can bind to erythrocytes, simultaneously with immune factors, causing hemagglutination and anemia.”⁶ “The important point is that some of the lectins consumed in everyday foods act as chemical messengers that can in fact bind to sugars in cells in the gut and the blood cells, initiating an inflammatory response. In wheat, gliadin, a component of gluten and isolectin of Wheat Germ Agglutinin (WGA), is capable of activating NFκB proteins which, when up-regulated, are involved in almost every acute and chronic inflammatory disorder including neurodegenerative disease, inflammatory bowel disease, infectious and autoimmune disease.”⁷ Celiac disease is an autoimmune disease characterized by immune dysfunction. It has been theorized that celiac disease may in part be related to carbohydrate-binding peptides such as the lectin WGA.⁸ Higher levels of wheat lectin specific antibodies have been detected in blood from individuals suffering from celiac disease compared to healthy individuals, indicating at least a secondary involvement of lectins in the disease.⁹

The modulation of immune function by dietary lectins has been implicated as a contributing factor in the development of rheumatoid arthritis. The proposed mechanism involves dietary lectins interacting with enterocytes and lymphocytes, which facilitates the translocation of both dietary and gut-derived bacterial antigens to peripheral tissues, which in turn cause persistent peripheral antigenic stimulation.¹⁰ “In genetically susceptible individuals, this antigenic stimulation may ultimately result in the expression of overt RA via molecular mimicry in which foreign peptides are similar enough in structure to cause T-lymphocytes and antibodies to cross-react with endogenous peptides and break immunological tolerance.”¹¹

Since lectins are ubiquitous and extensively distributed in nature, do they have a ‘good’ side? As you may suspect natural substances generally possess both beneficial and deleterious effects depending on the circumstances (e.g. hormesis). “Lectins found in animals are most often found to aid in cell interaction, while plant lectins are known to ward off potential predators or pathogens. However, all lectins share the property of involvement in both normal and pathological biological processes and all have varying degrees of interaction with the immune system.”¹² Certain lectins from animal and plant sources can induce apoptosis and autophagy of cancer cells and thus possess the potential of being developed into anticancer agents.¹³ An example of a plant lectin used clinically at low doses in the treatment of different cancers with what appears to be beneficial effects without serious side effects is mistletoe (Viscum album) lectin extract.¹⁴ High dose administration appears to be counterproductive.

¹ Hamid R, Masood A. Dietary Lectins as Disease Causing Toxicants. Pakistan J Nutri. 2009; 8(3): 293-303.

² Nachbar MS, Oppenhiem JD. Lectins in the United Sates diet; a survey of lectins in commonly consumed foods and a review of the literature. Am J Clin Nutr. Nov 1980; 33: 2238-2345.

³ Kjaer TMR, Frokiaer H. Dietary Lectins and the Immune Response. In: Preedy VR, Watson RR. Reviews in Food and Nutrition Toxicity. Volume 4. Boca Raton: CRC Press; 2005. p. 271.

⁴ D’Adamo PJ, Siminovich-Blok B. Nontransfusion Significance of ABO and ABO-Associated Polymorphisms. In: Pizzorno JE, Murray MT. Textbook of Natural Medicine. 4th Ed. St. Louis: Elsevier; 2013. p. 365.

⁵ Hamid R, Masood A. Dietary Lectins as Disease Causing Toxicants. Pakistan J Nutri. 2009; 8(3): 293-303.

⁶ Ibid.

⁷ Ibid.

⁸ Kjaer TMR, Frokiaer H. Dietary Lectins and the Immune Response. In: Preedy VR, Watson RR. Reviews in Food and Nutrition Toxicity. Volume 4. Boca Raton: CRC Press; 2005. p. 288.

⁹ Ibid.

¹⁰ Cordain L, Toohey L, Smith MJ, Hickey MS. Modulation of immune function by dietary lectins in rheumatoid arthritis. British Journal of Nutrition. 2000; 83: 207-217.

¹¹ Ibid.

¹² Yau T, Dan X, Wing Ng CC, Bun Ng T. Lectins with Potential for Anti-Cancer Therapy. Molecules. 2015; 20: 3791-3810.

¹³ Ibid.

¹⁴ Ibid.