What are Lectins and the Lectin-Free Diet?

by Brooklin White MS Candidate, Dietetic Intern Nutrition

The concept of lectins in the diet has received attention in recent years due to celebrity nutrition “experts” touting health claims of implementing a lectin-free diet. Below we break down what the science says in regards to the implications of consuming lectins.

What are Lectins?

Lectins are a type of carbohydrate binding protein present in nearly 30% of the foods that we eat including legumes, peanuts, lentils, potatoes, eggplant, tomatoes, fruits and wheat. Lectins act as a form of natural glue in plant foods, binding components of the plant together. Lectins have been consumed as a dietary staple through these plant rich foods for generations in various centenarian cultures, such as those found in Costa Rica, Italy and Greece (also known as the Blue Zones).

For the last several years there has been debate regarding lectins and whether or not lectin rich foods should be included as a part of a healthy diet. Recent pseudoscience fad books and articles claim that lectins are a major cause for autoimmune disease, obesity and chronic inflammation, however, there is little scientific evidence that shows eliminating dietary lectins will cure any medical disorders or conditions. In fact, many of the resources cited in these books include ProteinPower, The Beef Site, and other pseudoscience non-nutrition professionals - not credible sources for nutrition information.

Lectins and Inflammation

Lectin-free advocates claim that all lectins cause inflammation. While it is important to note that there are some lectins that can trigger an immune response, this only occurs with certain types of lectins in individuals with certain sensitivities, such as those with irritable bowel syndrome (1). It is important for individuals experiencing digestive issues to work with a registered dietitian nutritionist to identify potential food triggers. Science strongly suggests that eating a high plant-based diet, including many of the plants that contain not only lectins but also key nutrients, antioxidants and phytochemicals, actually has an anti-inflammatory effect on the body and has been associated with lower incidences of stroke, heart disease and oxidative stress (2). In other words, the wealth of nutrition research indicates that lectin rich foods have the exact opposite effect of what lectin-free proponents claim: that they actually reduce diseases associated with inflammation.

Lectins and Toxicity

Lectins are used as a defense mechanism in plants to protect themselves against fungus and bacteria yet serve no nutritional value when consumed in foods (3). One of the main concerns about eating lectins surrounds the idea that this natural defense mechanism can become toxic to the human system when eating large amounts of raw lectins. Although this is true in theory, the amount of raw lectins an individual would need to consume to see adverse effects is exponentially larger than a typical diet would include, especially since the majority of lectins found in beans and lentils are not consumed raw (4). Additionally, it has been shown that the majority of lectins denature or break down when well-soaked or cooked, ridding the plant of its potentially toxic nature (5,6).

Another important concept in regards to lectins is that of hormesis. The term hormesis has gained recent attention when it comes to the consumption of phytonutrients such as lectin. Hormesis refers to when a specific chemical is able to induce biologically opposite effects at different doses (7). The concept of hormesis states that when phytochemicals are consumed in modest amounts, we see the activation of beneficial biochemical pathways, yet if significantly over consumed, they can become noxious (8). The same phytochemicals that serve as natural pesticides for plants in nature, create a beneficial stress response in human cells when consumed in adequate doses. Similar stress responses are seen with exercise and calorie restriction - benefits are seen with consistent application yet they can cause exhaustion and cellular damage if over utilized. Phytochemicals encourage cellular strength and resilience by controlling when antioxidants are available to be used by cells, such as neurons (8). Curcumin which is the main phytochemical found in turmeric, does not function by neutralizing free radicals but rather by recruiting antioxidant enzymes which reduce free radicals and the accumulation of toxic proteins (8). Another example of hormesis is seen with Vitamin A. When consumed at daily recommended levels, Vitamin A is beneficial for the immune system, development, and eye health. When consumed in high doses however, such as through oral supplements, Vitamin A can exhibit a toxic effect and lead to a variety of health issues such as headaches, drowsiness, anorexia, changes in vision and bone pain (9). Lectins are just one of many phytochemicals found in plants and are no exception to the rule of hormesis. Although we do consume lectins with a plant based diet, we don’t eat enough to create harmful effects.

Lectins and Overall Health

The benefits of consuming lectin containing plants far outweigh any perceived benefits of a lectin-free diet. In fact, the problem with most Americans today is that they are not eating enough plant foods, which is why we are seeing a tremendous spike in chronic diseases such as obesity, diabetes, and Alzheimer’s. The western diet includes a high percentage of meat, dairy, sugars and processed foods which has been supported by scientific research over and over again to promote disease states, whereas plant-based foods do the exact opposite (10). The complex carbohydrates found in vegetables, whole grains, beans and whole fruit contain vital vitamins, minerals, fiber and phytonutrients that support our cellular function, blood glucose control, fat regulation, cognition and overall health.

Should I Focus on a Lectin-Free Diet?

The simple answer is no, unless you have a specific medical concern that is triggering symptoms related to the foods that you eat. For example, a recent review notes that a lectin-free diet may benefit people with inflammatory bowel disease and MS, but the research is not yet conclusive (1). Lectins have been consumed as a part of a healthy plant-based diet for centuries, especially by those who live in the Blue Zones and consistently live healthfully into old age. When considering nutrition advice, it is crucial to consider the source of nutrition information. The Amos Institute prides itself in looking at scientific information holistically by using the Five Pillars of Research, a concept introduced by Dr. Valter Longo. The Five Pillars of Research allow practitioners to look at nutrition science from every angle – are these nutrients or groups of nutrients supported by multiple facets of research? Do the animal studies, human studies, epidemiological data, and centenarian studies point to the same answer? When it comes to lectin containing foods, the answer is yes. The research proves over and over again that eating a plant based diet, including those containing lectins, are beneficial for a healthy body and mind. As lifestyle and preventive medicine Dr. David Katz once wrote, "...wherever [humans] eat mostly vegetables, fruits, whole grains, beans, lentils, nuts, and seeds, and drink mostly water, they tend to live long, prosper with vitality... It is not the job of “science” to tear down this established foundation: It is the job of science to build upon it." (11).

If you need more guidance regarding the type of diet you should eat to optimize brain health, sign up for the Amos Institute Cognitive Health Program today.


References

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  2. Holt, E. M., Steffen, L. M., Moran, A., Basu, S., Steinberger, J., Ross, J. A., Hong, C.-P., & Sinaiko, A. R. (2009). Fruit and vegetable consumption and its relation to markers of inflammation and oxidative stress in adolescents.Journal of the American Dietetic Association,109(3), 414–421.https://doi.org/10.1016/j.jada.2008.11.036
  3. Roos, N., Sørensen, J. C., Sørensen, H., Rasmussen, S. K., Briend, A., Yang, Z., & Huffman, S. L. (2013). Screening for anti-nutritional compounds in complementary foods and food aid products for infants and young children.Maternal & Child Nutrition,9(S1), 47–71.https://doi.org/10.1111/j.1740-8709.2012.00449.x
  4. Mayo Clinic Q and A: What are dietary lectins and should you avoid eating them?(2018, September 14). https://newsnetwork.mayoclinic.org/.https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-what-are-dietary-lectins-and-should-you-avoid-eating-them/
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  6. Rodhouse, J. C., Haugh, C. A., Roberts, D., & Gilbert, R. J. (1990). Red kidney bean poisoning in the UK: An analysis of 50 suspected incidents between 1976 and 1989.Epidemiology and Infection,105(3), 485–491.https://doi.org/10.1017/S095026880004810X
  7. Calabrese, E. J., Bachmann, K. A., Bailer, A. J., Bolger, P. M., Borak, J., Cai, L., Cedergreen, N., Cherian, M. G., Chiueh, C. C., Clarkson, T. W., Cook, R. R., Diamond, D. M., Doolittle, D. J., Dorato, M. A., Duke, S. O., Feinendegen, L., Gardner, D. E., Hart, R. W., Hastings, K. L., … Mattson, M. P. (2007). Biological stress response terminology: Integrating the concepts of adaptive response and preconditioning stress within a hormetic dose–response framework.Toxicology and Applied Pharmacology,222(1), 122–128.https://doi.org/10.1016/j.taap.2007.02.015
  8. Mattson, M. P. (2015). WHAT DOESN’T KILL YOU….Scientific American,313(1), 40–45.
  9. Penniston, K. L., & Tanumihardjo, S. A. (2006). The acute and chronic toxic effects of vitamin A.The American Journal of Clinical Nutrition,83(2), 191–201.https://doi.org/10.1093/ajcn/83.2.191
  10. Medawar, E., Huhn, S., Villringer, A., & Veronica Witte, A. (2019). The effects of plant-based diets on the body and the brain: A systematic review.Translational Psychiatry,9.https://doi.org/10.1038/s41398-019-0552-0
  11. Katz, D. L. (2019, March 18).We already know the best diet for humans. Medium.https://heated.medium.com/we-know-more-about-food-than-ever-before-d9266b0aabce