Lectin Toxicity: A Fact or Fad?

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When it comes to nutrition, it can be hard to distinguish facts from fads. You may have heard recently that lectins found in foods like beans and lentils are toxic and that eliminating lectins from your diet is the key to good health, but this is not the stance dietitians are taking.

What Are Lectins? 

Lectins are carbohydrate-binding proteins found in many plant-based foods like legumes, grains, certain veggies and fruits, coffee and spices. There are many different types of lectins, even in animal foods, each with different functions and effects on the body. Paleo diet proponents caution that plants produce lectins as toxins to protect themselves from being eaten by predators (like us). While there is some truth behind these claims—certain lectins are toxic to humans—there is limited research on which these claims are based.

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Should I Avoid Lectins?

Lectins can bind carbohydrates on cells throughout the digestive tract, damaging microvilli and impairing the absorption of nutrients. This damage may lead to the development of allergic reactions and autoimmune diseases. The good news is that these harmful effects are only found when beans are eaten raw or undercooked, which also causes vomiting and diarrhea. Conventional cooking methods used to prepare beans and legumes drastically reduces, and can even eliminate, their lectin content. According to PEN (Practice-based Evidence in Nutrition) there is no evidence of lectins in vegetables being harmful to us.

The lectin-free diet promoted by Loren Cordain, an outspoken Paleo advocate, and Steven Gundry, author of The Plant Paradox, forbids a long list of healthy foods including peppers, tomatoes, cucumbers, eggplant, squash, beans, lentils, soy, whole grains and dairy. This diet is very restrictive, and would be nearly impossible for a vegetarian or vegan to follow!

Contrary to the fear mongering about lectins promoting inflammation, disease and weight gain, there is strong evidence to support the many health benefits of lectin-containing foods. Whole grains, beans, and nightshade vegetables are found to have anti-inflammatory effects. Legumes are associated with improved weight management and metabolic status as well as reduced mortality (death) rates. Lectins may even have health benefits for cancer prevention. Eliminating these foods from your diet will increase your risk of nutrient deficiencies and is not recommended by dietitians.

How Can I Safely Eat Legumes?

To safely reduce lectins in raw legumes, prepare dried beans and lentils according to package directions. Lectins can withstand heating up to 50-55°C so avoid using a slow cooker when preparing beans and lentils from scratch. A slow cooker does not reach a high enough temperature to destroy lectins, so boiling is the best method.

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Conventional cooking methods used to prepare beans and legumes drastically reduces, and may even eliminate, their lectin content.

The Bottom Line

Any diet that scares you into eliminating a long list of healthy foods and claims to be a revolutionary cure-all is just a fad. Before trialling a new diet, it is best to consult a registered dietitian for trustworthy, evidence-based advice. 

Sources:

Cheng, H. M., Koutsidis, G., Lodge, J. K., Ashor, A., Siervo, M., & Lara, J. (2017). Tomato and lycopene supplementation and cardiovascular risk factors: A systematic review and meta-analysis. Atherosclerosis, 257, 100-108. doi:10.1016/j.atherosclerosis.2017.01.009

Mollard, R. C., Luhovyy, B. L., Panahi, S., Nunez, M., Hanley, A., & Anderson, G. H. (2012). Regular consumption of pulses for 8 weeks reduces metabolic syndrome risk factors in overweight and obese adults. British Journal of Nutrition, 108(S1). doi:10.1017/s0007114512000712

Sharon, N., Lis, H., & SpringerLink (Online service). (2007). lectins. Dordrecht: Springer Science+Business Media B.V.

Vitaglione, P., Mennella, I., Ferracane, R., Rivellese, A. A., Giacco, R., Ercolini, D., . . . Fogliano, V. (2014). Whole-grain wheat consumption reduces inflammation in a randomized controlled trial on overweight and obese subjects with unhealthy dietary and lifestyle behaviors: Role of polyphenols bound to cereal dietary fiber. The American Journal of Clinical Nutrition, 101(2), 251-261. doi:10.3945/ajcn.114.08812

Ryan Stallard