What do beans, grains, nuts, tomatoes, eggplant, and peppers have in common? They have been wrongfully accused of being dangerous because they contain lectin proteins. So say advocates of the Paleo diet websites and books loaded with misinformation. All of which can confuse and harm people who are already eating an insufficient amount of plant foods. What is harmful to our health is promoting this twisted information which has led to many people being afraid to eat health-promoting foods like beans and tomatoes.
Unfortunately, nutritional misinformation abounds and the consumption of health fortifying nutrient-rich plant foods in our society is dangerously low. The Centers for Disease Control and Prevention (CDC) has stated that 75% of healthcare spending goes to treating chronic diseases, most of which are preventable and diet-related. 1 .
To say lectins are “disease-causing” and that people need to avoid beans, vegetables and nuts in order to get healthy and lose weight, has been thoroughly disproven by the thousands of studies documenting the health and longevity benefits of these foods. .
The real story - what lectins do in our body
Lectins are proteins that bind carbohydrates. There are many different lectins, which have different functions because they bind to different carbohydrates. Lectins are not only present in plant foods; they are ubiquitous in nature – in plants, animals, and microorganisms.2
The main function of lectins in animals is to facilitate cell-cell contact – lectins on one cell recognize and bind to surface carbohydrates on another cell. In plants, the function of lectins is less clear but some lectins are thought to be plant defense proteins, to protect against pathogens and insects. 3 This is similar to other phytochemicals; flavonoids, for example, also serve as natural defenses in plants. 4
Potential benefits of plant food lectins
Plant lectins bind carbohydrates during digestion, slowing or preventing their breakdown, and thereby reducing the glycemic effects of the food. 5 This action of lectins is most likely a contributing factor to the pro-weight loss and anti-diabetes effects of beans and other plant foods. Beans are rich in fiber and anti-cancer phytochemicals and demonstrate a powerful association with lower rates of colorectal, prostate, and breast cancers.6-8
A lectin in common mushrooms has been found to inhibit proliferation of cancer cells in vitro.9,10 Mushrooms are another food offering powerful protection against cancer. ,11,12 And that’s not the only one: similar results have been found for lectins from fava beans, soybeans, bananas, buckwheat, jackfruit, and wheat.13-19 Some of these lectins are being investigated as potential cancer therapies.20,21 Certain plant food lectins may also help prevent cancer development by blocking the actions of angiogenesis-promoting lectins on human cells.20
Do lectins pose any dangers?
There is one lectin known to cause temporary gastrointestinal distress in humans called phytohemagglutinin; it is found in raw beans, red kidney beans in particular. However, it is easily avoided. This lectin is inactivated by cooking. If you use dry beans, take the necessary precaution of making sure they are thoroughly cooked – don’t eat undercooked beans.
Special cases of sensitivity to certain lectins
Some food allergies are allergies to a lectin specific to that food. Also, bacterial infections, inflammatory bowel disease (IBD), colon cancer, or autoimmune illnesses may alter intestinal cells in a way that makes usually harmless food lectins problematic. For example, wheat may be problematic for rheumatoid arthritis and peanuts for IBD and colon cancer. However, carbohydrates from dietary fiber could potentially block or reduce these harms.22,23 It is likely there are individuals who should avoid a specific food because of their individual response to a lectin in that food. But this does not mean that lectins are harmful for the general population.
Keep eating beans and tomatoes – they have huge health benefits
People who regularly eat beans have greater intakes of minerals and fiber, have lower blood pressure, and are less likely to be overweight than people that don’t consume beans.24 The consumption of beans is linked to lifespan enhancement, lower rates of cardiovascular disease, lower risk of colorectal and several other cancers.25-32
Tomatoes are the major source of the carotenoid lycopene, a strong antioxidant that helps protect the skin from UV damage. In addition, tomatoes have a number of cardiovascular system benefits including making LDL cholesterol more resistant to oxidation.36-38 Higher blood lycopene is associated with a lower risk of heart attack and stroke, and low blood lycopene are associated with a greater risk of premature death.39-43
Beans, vegetables, mushrooms, nuts and seeds are high-nutrient, fiber-rich foods that are consistently associated with beneficial health outcomes and a longer life. The hypothesis that these foods are harmful due to the negative effect of certain plant lectins is without scientific merit and not supported by the preponderance of evidence from nutritional research studies.
- National Center for Chronic Disease Prevention and Health Promotion, U.S. Centers for Disease Control and Prevention: The Power of Prevention 2009 [https://www.cdc.gov/chronicdisease/pdf/2009-Power-of-Prevention.pdf]
- Lectins Are Specific Carbohydrate-Binding Proteins. In Biochemistry 5th edition. Edited by Berg JM, Tymoczko JL, Stryer L: W H Freeman; 2002
- Lannoo N, Van Damme EJ. Lectin domains at the frontiers of plant defense. Front Plant Sci 2014, 5:397.
- War AR, Paulraj MG, Ahmad T, et al. Mechanisms of plant defense against insect herbivores. Plant Signal Behav 2012, 7:1306-1320.
- Rea RL, Thompson LU, Jenkins DJ. Lectins in foods and their relation to starch digestibility. Nutr Res 1985, 5:919-929.
- 6. Zhu B, Sun Y, Qi L, et al. Dietary legume consumption reduces risk of colorectal cancer: evidence from a meta-analysis of cohort studies. Sci Rep 2015, 5:8797.
- Trock BJ, Hilakivi-Clarke L, Clarke R. Meta-analysis of soy intake and breast cancer risk. J Natl Cancer Inst 2006, 98:459-471.
- Li J, Mao QQ. Legume intake and risk of prostate cancer: a meta-analysis of prospective cohort studies. Oncotarget. 2017 Jul 4;8(27):44776-44784.
- Yu L, Fernig DG, Smith JA, et al. Reversible inhibition of proliferation of epithelial cell lines by Agaricus bisporus (edible mushroom) lectin. Cancer Res 1993, 53:4627-4632.
- Carrizo ME, Capaldi S, Perduca M, et al. The antineoplastic lectin of the common edible mushroom (Agaricus bisporus) has two binding sites, each specific for a different configuration at a single epimeric hydroxyl. The Journal of biological chemistry 2005, 280:10614-10623.
- Li J, Zou L, Chen W, et al. Dietary mushroom intake may reduce the risk of breast cancer: evidence from a meta-analysis of observational studies. PLoS One 2014, 9:e93437.
- Ren L, Perera C, Hemar Y. Antitumor activity of mushroom polysaccharides: a review. Food Funct 2012, 3:1118-1130.
- Jordinson M, El-Hariry I, Calnan D, et al. Vicia faba agglutinin, the lectin present in broad beans, stimulates differentiation of undifferentiated colon cancer cells. Gut 1999, 44:709-714.
- Panda PK, Mukhopadhyay S, Behera B, et al. Antitumor effect of soybean lectin mediated through reactive oxygen species-dependent pathway. Life Sci 2014, 111:27-35.
- Singh SS, Devi SK, Ng TB. Banana lectin: a brief review. Molecules 2014, 19:18817-18827.
- Bai CZ, Ji HJ, Feng ML, et al. Stimulation of dendritic cell maturation and induction of apoptosis in lymphoma cells by a stable lectin from buckwheat seeds. Genet Mol Res 2015, 14:2162-2175.
- Yu LG, Packman LC, Weldon M, et al. Protein phosphatase 2A, a negative regulator of the ERK signaling pathway, is activated by tyrosine phosphorylation of putative HLA class II-associated protein I (PHAPI)/pp32 in response to the antiproliferative lectin, jacalin. J Biol Chem 2004, 279:41377-41383.
- Ebert C, Nebe B, Walzel H, et al. Inhibitory effect of the lectin wheat germ agglutinin (WGA) on the proliferation of AR42J cells. Acta Histochem 2009, 111:335-342.
- Schwarz RE, Wojciechowicz DC, Picon AI, et al. Wheatgerm agglutinin-mediated toxicity in pancreatic cancer cells. Br J Cancer 1999, 80:1754-1762.
- Ochoa-Alvarez JA, Krishnan H, Shen Y, et al. Plant lectin can target receptors containing sialic acid, exemplified by podoplanin, to inhibit transformed cell growth and migration. PLoS One 2012, 7:e41845.
- Liu B, Bian HJ, Bao JK. Plant lectins: potential antineoplastic drugs from bench to clinic. Cancer Lett 2010, 287:1-12.
- Freed DL. Do dietary lectins cause disease? BMJ 1999, 318:1023-1024.
- Ryder SD, Smith JA, Rhodes JM. Peanut lectin: a mitogen for normal human colonic epithelium and human HT29 colorectal cancer cells. J Natl Cancer Inst 1992, 84:1410-1416.
- Papanikolaou Y, Fulgoni VL, 3rd. Bean consumption is associated with greater nutrient intake, reduced systolic blood pressure, lower body weight, and a smaller waist circumference in adults: results from the National Health and Nutrition Examination Survey 1999-2002. J Am Coll Nutr 2008, 27:569-576.
- Darmadi-Blackberry I, Wahlqvist ML, Kouris-Blazos A, et al. Legumes: the most important dietary predictor of survival in older people of different ethnicities. Asia Pac J Clin Nutr 2004, 13:217-220.
- Marventano S, Izquierdo Pulido M, Sanchez-Gonzalez C, et al. Legume consumption and CVD risk: a systematic review and meta-analysis. Public Health Nutr 2017, 20:245-254.
- Lanza E, Hartman TJ, Albert PS, et al. High dry bean intake and reduced risk of advanced colorectal adenoma recurrence among participants in the polyp prevention trial. J Nutr 2006, 136:1896-1903.
- Singh PN, Fraser GE. Dietary risk factors for colon cancer in a low-risk population. Am J Epidemiol 1998, 148:761-774.
- Bessaoud F, Daures JP, Gerber M. Dietary factors and breast cancer risk: a case control study among a population in Southern France. Nutr Cancer 2008, 60:177-187.
- Aune D, De Stefani E, Ronco A, et al. Legume intake and the risk of cancer: a multisite case-control study in Uruguay. Cancer Causes Control 2009, 20:1605-1615.
- Zhu B, Sun Y, Qi L, et al. Dietary legume consumption reduces risk of colorectal cancer: evidence from a meta-analysis of cohort studies. Sci Rep 2015, 5:8797.
- Li J, Mao QQ. Legume intake and risk of prostate cancer: a meta-analysis of prospective cohort studies. Oncotarget 2017, 8:44776-44784.
- Bazzano LA, Thompson AM, Tees MT, et al. Non-soy legume consumption lowers cholesterol levels: a meta-analysis of randomized controlled trials. Nutrition, metabolism, and cardiovascular diseases : NMCD 2011, 21:94-103.
- Streppel MT, Arends LR, van 't Veer P, et al. Dietary fiber and blood pressure: a meta-analysis of randomized placebo-controlled trials. Arch Intern Med 2005, 165:150-156.
- Keku TO, Dulal S, Deveaux A, et al. The gastrointestinal microbiota and colorectal cancer. Am J Physiol Gastrointest Liver Physiol 2015, 308:G351-363.
- Rissanen T, Voutilainen S, Nyyssonen K, Salonen JT. Lycopene, atherosclerosis, and coronary heart disease. Exp Biol Med (Maywood) 2002, 227:900-907.
- Silaste ML, Alfthan G, Aro A, et al. Tomato juice decreases LDL cholesterol levels and increases LDL resistance to oxidation. Br J Nutr 2007, 98:1251-1258.
- Hadley CW, Clinton SK, Schwartz SJ. The consumption of processed tomato products enhances plasma lycopene concentrations in association with a reduced lipoprotein sensitivity to oxidative damage. J Nutr 2003, 133:727-732.
- Karppi J, Laukkanen JA, Makikallio TH, Kurl S. Low serum lycopene and beta-carotene increase risk of acute myocardial infarction in men. Eur J Public Health 2011.
- Karppi J, Laukkanen JA, Sivenius J, et al. Serum lycopene decreases the risk of stroke in men: A population-based follow-up study. Neurology 2012, 79:1540-1547.
- Sesso HD, Buring JE, Norkus EP, Gaziano JM. Plasma lycopene, other carotenoids, and retinol and the risk of cardiovascular disease in women. Am J Clin Nutr 2004, 79:47-53.
- Shardell MD, Alley DE, Hicks GE, et al. Low-serum carotenoid concentrations and carotenoid interactions predict mortality in US adults: the Third National Health and Nutrition Examination Survey. Nutr Res 2011, 31:178-189.
- Rissanen TH, Voutilainen S, Nyyssonen K, et al. Low serum lycopene concentration is associated with an excess incidence of acute coronary events and stroke: the Kuopio Ischaemic Heart Disease Risk Factor Study. Br J Nutr 2001, 85:749-754.