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Lectins. Have you heard of them before? They aren’t a word I’ve just made up, they’re naturally occurring compounds and they are causing quite a stir. I wish I could say if you haven’t heard of them don’t worry, though with how often I’m being asked about them, you are probably best of knowing how to sift through this information.
What are they?
Lectins are a group of proteins that bind to carbohydrates. They exist in plants and help to protect against external pathogens, like fungi.
Where do you find lectins?
Where don’t you find them! They are found in many foods including:
Legumes: lentils, chickpeas, beans, peanuts
Grains: wheat, rice, corn
Fruits: cherries, blackberries
Vegetables: tomato, potatoes, eggplant, pumpkin
Dairy
Some herbs and spices: peppermint, parsley
What’s the problem with them?
Basically, this is a perfect example of where a small piece of truth has been misconstrued and becomes a difficult web to untangle.
Lectins have become a talking point since Dr Steven Gundry, author of ‘The Plant Paradox’ claimed that due to lectins being stable in acidic environments and as such, not broken down during digestion, that intake of lectins leads to inflammation and a plethora of health issues.
Concerns about lectins
First things first
It is important to emphasise that these claims are not based on current evidence and that this can be the harm in isolating an element of truth to broadly draw conclusions.
Generally, foods that are higher in lectins are not consumed in a way that provide a high intake of lectins- for example boiling beans before consumption reduces level of lectins and reduced their binding ability significantly, as does canning beans. When’s the last time you ate raw beans?
Isolated lectins would not be fun; however, this is not a normal occurrence for humans. Cooking, soaking, canning, dehulling or sprouting foods containing lectins will reduce the amount and weaken the action of lectins.
Now, let’s look at the concerns more closely…
They can be dangerous to consume
Lectins can be dangerous. For example, ricin is a type of lectin found in castor beans and well known to be toxic to humans.
Another popular example is raw or undercooked kidney beans containing a type of lectin called phytohaemagglutinin, which causes red blood cells to clump together and has been documented to cause vomiting, nausea, and diarrhoea. Lesser effects including bloating and gas. However, this is only applicable to lectins in their active state- since red kidney beans aren’t usually consumed raw, it’s hardly relevant. Again, remembering that cooking or canning kidney beans would significantly reduce the lectin content and make them safe to consume.
Take away: Some types of lectins can be toxic. However, they are not relevant to how we consume lectin-containing foods. Cook, soak or buy canned beans and you’re covered!
They can have anti-nutrient effects
A common argument against lectins is that they can act as ‘anti-nutrients’ by interfering with the absorption of nutrients such as calcium, iron and zinc by binding to the intestinal wall.
This sounds far worse than it is, as plant foods contain a variety of ‘anti-nutrients’ most popular (after lectins lately) is phytates, which I’ve also written a little about here.
Generally, if a diet is high in these foods, as if someone is vegetarian, we would aim to have a higher intake of these nutrients to consider possible reductions in absorption.
Take away: Lectins are not the only ‘anti-nutrient’ in plant foods, they may impact nutrient absorption, but that doesn’t related to the ‘healthfulness’ of a food.
They are reported to be linked to inflammation + disease
Inflammation and disease are two other common claims pushing for a lectin-free diet. Really, there is very little evidence to refer to here, particularly if we were to look for human studies.
This is again, another good example of how information can be misconstrued. For example, in-vitro studies (of isolated cells) have shown inflammation when mixing human blood cells with lectin-containing wheat-germ, but this does not apply to real life circumstances. In fact, whole grains have consistently been linked to reduced inflammation.
The closest evidence we have, that is in reference to humans and lectins, shows that diets higher in plant foods (or “plant-based” as every product is currently labelled) including whole grains, legumes, fruit and vegetables, nuts and seeds is associated with a lower risk of disease and inflammation.
Consistently, diets following these plant-rich patterns are linked to better health outcomes, which does contradict such claims, and perhaps shows little benefit in jumping to such drastic conclusions…or rather more harm should people avoid these foods due to such fears?
Take away: There is very little human evidence relating to lectins and disease. Evidence does however support plant-rich diets for the reduction of disease, including those foods which contain lectins.
They are resistant to digestion
By far, digestion is one of the most common reasons I am asked about lectin-free diets.
Again, the element of truth is that lectins are not broken-down during digestion, however this does not mean they are harmful.
A related example is fibre. Fibre is the edible part of plants that is resistant to digestion by us, and travels down our digestive tract to then actually be completely or partially digested by out gut bugs, not us. A sudden increase in fibre can result in digestive symptoms like gas and bloating, thanks to these gut bugs, however these cases are linked to reduced risk of colon cancer.
An important factor to consider with the claims of a lectin-free diet improving digestive symptoms is that there are many factors that can result in symptoms like bloating, gas and diarrhoea- including fibre. FODMAPs are a group of dietary sugars that can cause IBS-like symptoms, and worsen IBS for many sufferers, though many of these foods overlap with lectin-containing foods.
It is important to determine actual triggers and include as much variety in a diet to ensure it is balanced, sustainable and also, nourishing our gut bugs! If you are reacting to foods containing lectins, but the lectin content is significantly reduced, perhaps it’s worth looking elsewhere.
Take away: Lectins are poorly digested; however, this does not mean they are harmful. If experiencing digestive symptoms, a reduction in lectin-content may be relevant, however there are many factors to consider, and improvements may be due to unknowingly reducing intake of common digestive triggers.
Health Benefits
Lectins may be getting a bad wrap of late, but when it comes to evidence, there is actually some supporting the use of lectins for human benefit!
Lectins may benefit our gut health and provide prebiotics, helping to nourish our gut bugs and improve digestive health read – this has furthermore been associated with reduced risk of disease and improved mental health
Lectins slow down digestion of carbohydrates and as such, reducing blood sugar spikes
Lectins in mushrooms may have anticancer properties (still early stages of research) and are being researched for anti-tumour use
Some lectins act as antioxidants protecting our cells from damage
Consistently, fruit and vegetables, legumes and whole grains have been linked to improved health outcomes including reduced risk of heart disease, type 2 diabetes cancer, all-cause mortality and reduced inflammation
Lectin-containing foods often provide protein, fibre, b-vitamins and minerals
Conclusion
Yes, please ensure you reduce your lectin content in dry beans by soaking them before consuming. In the way that most lectin-containing foods are prepared for consumption, the lectin content is significantly reduced and safe. Not that lectins are all bad, there is evidence supporting lectins for human benefit!
It will be interesting to watch the research regarding lectins over time. There is not current evidence supporting a diet that is low in plant foods and restricting lectin intake generally. However, evidence strongly supports that these foods are beneficial and linked to overall reduced risk of chronic disease.
References
Aune D, Keum N, Giovannucci E, Fadnes L T, Boffetta P, Greenwood D C et al. Whole grain consumption and risk of cardiovascular disease, cancer, and all cause and cause specific mortality: systematic review and dose-response meta-analysis of prospective studies BMJ 2016; 353 :i2716 doi:10.1136/bmj.i2716
de Munter JSL, Hu FB, Spiegelman D, Franz M, van Dam RM (2007) Whole Grain, Bran, and Germ Intake and Risk of Type 2 Diabetes: A Prospective Cohort Study and Systematic Review. PLOS Medicine 4(8): e261. https://doi.org/10.1371/journal.pmed.0040261
Freed D. L. (1999). Do dietary lectins cause disease?. BMJ (Clinical research ed.), 318(7190), 1023–1024. https://doi.org/10.1136/bmj.318.7190.1023
Liu Z, Luo Y, Zhou TT, Zhang WZ. Could plant lectins become promising anti-tumour drugs for causing autophagic cell death? Cell Prolif. 2013 Oct;46(5):509-15. doi: 10.1111/cpr.12054. Epub 2013 Aug 24. PMID: 24033443; PMCID: PMC6495496.
Peumans, W. J., & Van Damme, E. J. (1995). Lectins as plant defense proteins. Plant physiology, 109(2), 347–352. https://doi.org/10.1104/pp.109.2.347
Schwingshackl, L., Hoffmann, G., Lampousi, AM. et al. Food groups and risk of type 2 diabetes mellitus: a systematic review and meta-analysis of prospective studies. Eur J Epidemiol 32, 363–375 (2017). https://doi.org/10.1007/s10654-017-0246-y
Singh RS, Kaur HP, Kanwar JR. Mushroom lectins as promising anticancer substances. Curr Protein Pept Sci. 2016;17(8):797-807
Van Buul & Brouns (2014) “Health effects of wheat lectins: A review” [accessed January 2019 via: https://www.sciencedirect.com/science/article/pii/S0733521014000228
Vasconcelos IM, Oliveira JT. Antinutritional properties of plant lectins. Toxicon. 2004 Sep 15;44(4):385-403. doi: 10.1016/j.toxicon.2004.05.005. PMID: 15302522.
Vasconcelos IM, Oliveira JT. Antinutritional properties of plant lectins. Toxicon. 2004 Sep 15;44(4):385-403. doi: 10.1016/j.toxicon.2004.05.005. PMID: 15302522.
Venter FS, Thiel PG. Red kidney beans--to eat or not to eat? S Afr Med J. 1995 Apr;85(4):250-2. PMID: 7777998.
Vitaglione P, Mennella I, Ferracane R, Rivellese AA, Giacco R, Ercolini D, Gibbons SM, La Storia A, Gilbert JA, Jonnalagadda S, Thielecke F, Gallo MA, Scalfi L, Fogliano V. 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. Am J Clin Nutr. 2015 Feb;101(2):251-61. doi: 10.3945/ajcn.114.088120. Epub 2014 Dec 3. PMID: 25646321.
Vojdani A. Lectins, agglutinins, and their roles in autoimmune reactivities. Altern Ther Health Med. 2015;21 Suppl 1:46-51. PMID: 25599185.
Xu Y, Wan Q, Feng J, Du L, Li K, Zhou Y. Whole grain diet reduces systemic inflammation: A meta-analysis of 9 randomized trials. Medicine (Baltimore). 2018 Oct;97(43):e12995. doi: 10.1097/MD.0000000000012995. PMID: 30412134; PMCID: PMC6221555.