1. Lectins and their role in autoimmunity & related disorders
2. Did you ever hear about the blood type diet?
3. How do I decrease my lectin exposure?
4. Conclusion
If you have been following in Part 1 and Part 2 of this blog series, you will have a good grasp on what lectins are, what foods they are in, and how they cause inflammation. In this blog we will discuss the role of lectins in specific diseases and inflammatory conditions as well as provide useful information for those who would like to eliminate lectins from their diets.
Lectins and their role in autoimmunity & related disorders
Rheumatoid arthritis:
Lectins not only interact with muscles, but are also capable of interacting with the joints (1). The lectin found in wheat has been shown to bind to the patella (knee joint), and the soybean and peanut lectin are capable of binding to cartilage as well (1). When the lectins bind to the cartilage it is thought that they promote inflammation, possibly through auto-immune mechanisms (1). Research was being done to observe whether lectins played a role in the development of rheumatoid arthritis, although this has not been confirmed (1).
Normal IgG molecules (a normal component of the immune system) contain a sugar molecule called galactose. Galactose is missing from the side chains of IgG molecules in the case of Rheumatoid Arthritis (4). As a result, a molecule called N-acetyl glucosamine is exposed on the IgG instead of the galactose. Galactose deficient IgG antibodies present in the circulation are correlated with symptoms from Rheumatoid Arthritis (4). It happens to be that the wheat lectin contains N-acetyl glucosamine and is a trigger food (makes symptoms worse) in diet responsive Rheumatoid Arthritis (4). Furthermore, there is evidence that when lectins interact with the gut their distribution into peripheral tissues like the joints can be enhanced, setting the stage for an autoimmune condition like Rheumatoid-Arthritis. It is believed that by eliminating the stimulatory antigens (foods containing lectins), it will allow the immune system to cool down and reduce the symptoms in some patients with Rheumatoid Arthritis (4).
Post-infectious disorders:Generally, we don't develop autoimmunity or disease after consuming lectins only once. This is evident because they are a major part of the American diet. The reason for this is because we have a wide variety of molecules on our digestive tract for lectins to interact with, and also because we have a protective barrier that helps protect the receptors and cells that lectins will interact with (4). When we have viruses like the flu (influenza) or strep throat (streptococci), these viruses and bacteria contain neuraminidase, an enzyme that Is able to strip off the protective coating on our digestive tract (made from sialic acid molecules). It is postulated that diseases like diabetes or rheumatoid arthritis may come on immediately after an illness (4).
IgA NephropathyWheat lectin is also capable of binding to the glomerular capillary walls, mesangial cells, and renal tubules which is just fancy for saying "the kidneys" (4). Wheat lectin can bind to IgA (just another piece of the immune system) and induces cause the IgA to deposit in the kidneys in rat studies. This is thought to contribute to IgA nephropathy (an autoimmune kidney disease). Children with IgA nephropathy were placed on a gluten avoidance diet (no wheat lectin) and the result was reduced protein in the urine (proteinuria) and reduced immune complex (IgA) levels, hence a positive outcome (4).
Type I Diabetes/Autoimmune Thyroid DisordersLectins are able to stimulate HLA class II antigens on the pancreas (pancreatic islet cells) and thyroid cells that normally do not express these antigens (4). Antigens are simply put, little name tags on the cell surfaces that help with recognition. N-acetyl lactosamine is a sugar molecule that helps with binding to tomato lectin, and likely wheat, potato, and peanut lectin but also helps auto-antibodies bind to the islet cells of the pancreas, making an autoimmune response likely (4).
Peptic Ulcer DiseaseLectins are able to cause a release in histamine from the mast cells in the stomach. The histamine release initiates the secretion of stomach acid, which may play a role in the pathogenesis (disease development) of Peptic Ulcer Disease (4).
Viral Upper Respiratory InfectionsBecause lectins are known to be able to strip away the mucosal lining (the intestinal lining), allergists who recommend diets absent of starchy foods (starchy foods generally contain lectins) have anecdotally conferred protection to their patients against upper respiratory viral infections (4). It is thought that consuming less lectins will allow the nasopharyngeal (nose) and throat mucus linings to be more intact, therefore being more protective against viruses (4).
Did you ever hear about the blood type diet? The blood type diet proposed by D'Adamo specifies a different diet for the four main blood types (A,B,AB,O), depending on how the lectins of food would interact with the blood cells of different blood type groups (1). Many lectins are able to cause blood cells to agglutinate, or clump together which is the basis behind this diet. The thought is that by eating specific foods with lectins, they will be absorbed into the blood stream, interact with the blood cells, and form clots that could be harmful or fatal. As of 2015, there is not a connection between blood type, lectin consumption, and poor health (1).
How do I decrease my lectin exposure? Hopefully you are weighing the pros and cons of lectins based on all of the information discussed above. There is more and more evidence coming out about the avoidance of lectins, as well as the increased push towards ketogenic, paleo, and carnivore diets which are in large part devoid of lectins. If you find yourself desiring to decrease your lectin consumption, lectin avoidance through dietary choices can be the first step to protecting yourself from the potential negative effects of a high lectin diet. This would include eliminating many of the common legumes and grains that contain high concentrations of lectins. For this, I encourage you to either look at the section of this blog series that lists the foods that contain lectins, or go to Dr. Gundry's site and check out the "yes list" and "no list" where he has a detailed lists of foods that he recommends to consume or avoid. (Here is the link)
Furthermore, because there is a possibility that certain infections can decrease our protective ability from lectins, there may be some truth behind the notion of fasting when having a fever. Fasting may be protective by reducing the exposure of lectins to a weakened gut/immune system that could otherwise lead to an autoimmune response (4).
It should also be noted that most lectin proteins are degraded when exposed to adequate heating. Therefore, vegetables, fruits, and nuts contain a higher concentration of biologically active lectins when they are raw rather than cooked (1). In podcasts by Dr. Gundry, I have heard him emphasize the reason that ancient cultures soaked their beans was to decrease the lectin burden from the beans. Additionally, this is the same reason that the Asian cultures removed the hull from the rice, making white rice to remove the seed coat that is particularly high in lectins. He also mentions how pressure cooking foods like tomatoes helps to denature the lectins, rendering them edible. However, when asked about the nutritional safety of things like tomatoes after they have been cooked, I believe his response was something along the lines of "why would I want to eat something that is intended to be harmful to me anyway?" Although we have created work-arounds to the lectin issue like pressure cooking or removing the seeds and skins from certain foods (tomatoes and cucumbers) it should still make us question the initial reasons for consuming the particular lectin-containing food in the first place, especially if we have other options.
Certain seaweed and mucilaginous (gelatinous-like) vegetables such as okra are able to bind lectins, making them unable to interact with the cells lining the gut. Additionally supplementation with N-Acetylglucosamine (NAG) may help bind to the lectins in the digestive tract rather than having the lectins enter the circulation and bind to the NAG that is present in connective tissues like in joints (4). Some bacteria that cause urinary tract infections have lectins that like to bind to mannose, a sugar located on the cells that line the bladder. By supplementing with D-mannose, this may decrease the propensity for urinary tract infections.
Conclusion
Plant lectins are proteins found in many plants that are found in our diets today. Examples include wheat, corn, soy, peanut, and tomatoes. Lectins like to bind to sugar molecules throughout our body, but most specifically in our gastrointestinal tract where they are first absorbed. Plant lectins are able to increase the permeability (leakiness) of the gut, allowing antigens from food and microbes to enter the general circulation. The circulating lectins contribute to IgG and IgM antibody production (immune system response), modulate leukocyte function, while also binding to receptors like insulin and growth factor receptors, causing a disruption in their normal function, increasing intestinal growth, contributing to interference of repairing the gut lining, altering the microbiome, and promoting mitochondrial damage associated with inflammatory diseases, (1,2,3,4). Furthermore, high concentrations of lectins are also able to decrease tumor growth and cancer in several instances (1). Due to their nature, it is believed that lectins are contributing to the development of food intolerance, food allergy, and inflammatory diseases like inflammatory bowel disease, insulin-dependent diabetes, rheumatoid arthritis, celiac disease, post-infectious disorders, upper respiratory infections, peptic ulcer disease, and IgA nephropathy (3,4). Decreasing one's lectin consumption can be achieved by avoiding refined starchy foods (rice, pasta, potatoes ,tortillas, pastries, cookies, cereal, sugar), certain vegetables (tomatoes, cucumbers, peas, legumes, green beans, soy), specific nuts & seeds (pumpkin, sunflower, chia, peanuts, cashews), certain dairy (A1 dairy products including yogurt, cheese, ricotta, cottage cheese, kefir, and casein proteins), meat, poultry, or seafood fed grains or soy, grains (whole grains, oats, wheat, quinoa, rye, rice, buckwheat, corn), and certain oils (soy, grapeseed, corn, peanut, cottonseed, safflower, sunflower, and partially hydrogenated vegetable or canola oil).
1. Aricigil, Selma and Pryme, Ian F. 2015. Potential Beneficial Effects of Dietary Plant Lectins on Health. Natural Products: Research Reviews. 2: 1-27.
2. Vasconcelos, IM and Oliverra, JT. 2004. Antinutritional properties of plant lectins. Toxicon. 44(4): 385-403.
3. Gong, Tao et al. 2017. Plant Lectins Activate the NLRP3 Inflammasome To Promote Inflammatory Disorders. The Journal of Immunology. 198: 2082-2092.
4. Hamid, Rabia and Masood, Akbar. 2009. Dietary Lectins as Disease Causing Toxicants. Pakistan Journal of Nutrition. 8(3): 293-303.
5. Dr. Steven Gundry. 2017. Dr. Gundry Approved Foods (a print-friendly list). Retrieved: May 20, 2019. From: https://gundrymd.com/plant-paradox-shopping-list/
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