Are all lectins bad? (and what are lectins, anyway?)

January 11, 2014 in Categories: , , by

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Full of lectinsThe word “lectin” is often misused within the paleo community.  You’ll hear phrases like “grains are bad because they’re full of lectins”.  While this is basically true, not all lectins are bad.

Lectins are a large class of carbohydrate-binding proteins found in all forms of life, including the human body.  Many types of receptors embedded in the cells in our bodies are lectins.  A group of proteins essential to our innate immune systems, called complement proteins (because they “complement” the activities of inflammatory cells by providing a rudimentary targeting mechanism for this otherwise non-specific part of the immune system), are lectins. This is why labeling a food as “full of lectins” is inaccurate and the type of phrase that opens up the Paleo diet to (valid) criticism.

In plants, the roles of lectins are still being identified, although they appear to be part of the plants’ natural defense mechanisms and to be important for seed survival (why lectins tend to be concentrated in the seeds of plants).

Not all lectins are bad, but some are (or at least, can be). A subset of lectins that can be found in large concentrations in the seeds of grasses (i.e. grains) and the legume family do have some properties that can make them very problematic for human health, namely that:

  1. they are hard to digest (this has the effect that they can overfeed certain species of gut bacteria and lead to gut dysbiosis, which now linked to a variety of health conditions),
  2. they can interact with the gut barrier and actually damage the cells that form the gut barrier or open up the junctions between those cells (genetic susceptibility plays a role in what extent this happens in your body), contributing to development of a leaky gut (now linked to a variety of health conditions), and
  3. they can stimulate the immune system (proportional to how much enters the body and type of lectin).

There are really just two classes of lectins that are known to be problematic for human health and have the above properties.  The first are called prolamins (gluten is an example of a prolamin), so called because of their rich proline (an amino acid) content.  The second are called agglutinins (wheat germs agglutinin, kidney bean lectin, and soy lectin are examples of agglutinins), so called because of their strong ability to agglutinate (or make clump together) red blood cells (they also happen to be rich in proline).

Phytohemagglutinin, also known as kidney bean lectin.

Both prolamins and aglutinins (there are many many proteins within each class) affect the type of bacteria that like to grow in your gut (in a negative way, typically preferentially overfeeding certain strains like E. coli).  They are also very good at crossing the gut barrier and there are actually four known mechanisms through which prolamins can enter the body (one of which is dependent on genetic susceptibility and it remains unknown if the other three occur in everyone or vary from person to person) and three known mechanisms through which agglutinins can enter the body (which appear to be independent of genetics, although more studies are required).  Not all of these entry pathways damage the gut barrier, but some can (again, genetic susceptibility may play a role, but more research is needed). By the way, I should mention that the exact mechanisms of how these proteins enter the body and potentially damage the gut barrier are discussed in detail in The Paleo Approach (in a way that anyone can understand with illustrations, so don’t let that intimidate you either!).  Once these proteins enter the body, they interact strongly with the immune system (typically stimulating inflammation, but the adaptive immune system can also be affected).

The distinction between prolamins, agglutinins and lectins in general is why you’ll see more and more people within the paleo community using the term “toxic lectin” or being even more specific and using the terms prolamin and agglutinin.  However, even within these two classes, some prolamins and agglutinins are more damaging than others.

For example, the agglutinins in many types of legumes can be reduced by soaking, sprouting and fermenting and largely deactivated by heat, especially during prolonged cooking.  And the concentration of agglutinins in different types of legumes varies dramatically.  In fact, legumes with edible pods like green beans, sugar snap peas and snow peas are generally endorsed on a paleo diet because the concentration of agglutinins is low and the instability of the agglutinins in these legumes means they are typically rendered inactive by cooking. In other types of legumes (soy and peanuts being the biggest culprits, but also some types of dried beans like kidney beans), the agglutinins are very resistant to deactivation and degradation.  Wheat germ agglutinin is so resistant to deactivation through even traditional food preparation methods, that even consumed as part of your food, it qualifies as a biologically active compound in our digestive tracts (that would not be a normal classification for a protein in food!).

There are no comprehensive studies that measure the amount or the different types of prolamins and agglutinins in different grains and legumes or their stability with different food preparation methods.  Until these details are better understood, the Paleo diet omits all grains and all legumes (with the exception of those with edible pods as already mentioned) due to the potentially detrimental effects of prolamins and agglutinins on human health.   It also doesn’t help that these are high glycemic load foods, with incomplete protein that is harder to digest than animal protein, and with lower vitamin, mineral and antioxidant density than fruit and vegetables (which is what a Paleo diet endorses consuming instead of grains and legumes, and something I personally feel very passionately about including in large amounts in my own diet).

So now you know that it’s more accurate to say “I don’t eat grains because they contain prolamins and agglutinins”…  although admittedly, that doesn’t roll of the tongue as easily!

Essentials of Glycobiology. Chapter 30 (Plant Lectins)  Varki A, Cummings R, Esko J, et al., editors.  Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 1999.  http://www.ncbi.nlm.nih.gov/books/NBK20717/

Vasconcelos IM, Oliveira JT.  Antinutritional properties of plant lectins. Toxicon. 2004 Sep 15;44(4):385-403. http://www.ncbi.nlm.nih.gov/pubmed/15302522

Mechanisms of interaction with the gut barrier and the immune system are summarized with dozens of references in The Paleo Approach.

Comments

Hi, thanks so much for this article, which was extremely informative on a topic that I’m just beginning to learn about!

I just bought Sun Warrior brand “Warrior Blend” protein powder. It contains pea protein (and the peas were picked from the plant while still full of moisture, not dried – I emailed them to ask), hemp protein, cranberry protein, and coconut MCT’s.

Is this protein powder, then, potentially troublesome for someone on the AIP diet to heal their gut, because of the pea protein? Apparently, it is uncooked.

Thanks for all your wonderful guidance!

~ Antonia

I would generally say that this protein powder is probably fine for someone following a standard paleo diet and potentially problematic for someone who needs to follow the AIP (both due to the pea protein and the hemp protein). You might still want to experiment with it and see if it works for you, but I would suggest caution.

Oh, my goodness! It didn’t take you long at ALL to reply to me! I’m so profoundly grateful, and appreciate your sage advice on this matter! I am definitely following the AIP. I’m dismayed because I had been hoping that the pea protein might be similar enough to the snap peas and sweet peas mentioned as “safe” for AIP – oh, well. It has been mentioned on Hashi’s 411 and if you don’t mind, I’ll pass along your reply to those on AIP who are considering it.

Thank you again! Looking forward to your book! I bought the cookbook e-book already, and have loved the recipes made from it. I look forward to the cookbook being in hardcover sometime.

Wow! Super interesting. I have been following an almost paleo diet for about a year now, and have always had a very vague understanding of why grains and legumes aren’t included. I’m curious if you know how one can tell if prolamins and agglutinins really cause a negative reaction in their body? Obviously they are detrimental to everyone, but do the symptoms vary? For instance, I find that I have a lot of problems with soy, but can eat peanut butter for days and FEEL fine.
I will definitely be pre-ordering your book. This is incredibly valuable information!

Thanks!

For some people, the reactions are obvious (especially after an elimination diet). But for others, the build-up of the effects of these proteins could be what contributes to diseases we consider to be part of aging. Still others might tolerate them just fine. It’s still unclear to what extent genetics (and other diet and lifestyle factors) play a role (for example, stress plus prolamins may be the problem).

I have been on the paleo diet for 5 months now. I have celiac disease, fibro, and lots of food intolerance issues. I always thought peanut butter was one of my best, most safe foods. I don’t see any digestive reaction to it. Does that mean it is OK for me or can it still cause leaky gut with no obvious symptoms? I am looking forward to buying your book!

Peanut lectin is a very potent immune stimulator. If you started with “I’m perfectly healthy”, I would say “If it’s working for you, go for it”. But, if you’re having issues with immune and autoimmune conditions, I think a peanut-free trial would be good idea.

Are scientists concerned about the lectins in fresh green beans? I realize they’re part of the kidney bean family. Does steaming green beans help destroy lectins? Or must they be boiled?

And what’s the deal with nuts and seeds? Are scientists concerned about the lectins in any nuts or seeds? Does soaking help remove them? What about pumpkin seeds?

Thanks so much for all your hard work.

Susan, I have also a lot of food intolerance, however no digestive issues.
For instance, my gluten intolerance primary symptom is dermatitis. I removed dairy products from my diet and my extremely severe menstrual pains became moderate. I transitioned to the paleo diet (the standard dairy free version, not AIP), and I’m really feeling better. I went paleo to try to repair my messed up hormones, that’s just my weak point. Other people might have healthy hormones and a laundry list of digestive issues. We are all different, so no digestive complaints does not necessarily mean that a food is OK.
I find that this point is too often not stressed enough in the “alternative diets” (paleo and others) as the focus is so much on digestive issues and sometimes it’s forgotten that someone can have no digestive issues and still benefit from a gut healing diet.

Lentils are a HUGE part of the diet of a HUGE population of people in Asia, where I happen to live. Any thoughts/info on the agglutinins or other issues of lentils?

There are several options:

1) print it
2) print it and save to PDF instead (if you want to save the paper, ink, and need to “file” it)
3) use the links at the bottom of article to email it to yourself
4) use the links to post it to your FB or Google account (sharing will keep it in your feed)
5) if you use a Mac and Safari, click the “+” button by the URL to add it to your reading list
6) use an offline reader like Instapaper
7) save the URL to your bookmarks
8) copy the URL and save it into a “research” page of your digital notebook (e.g. OneNote)
9) probably other options, too…

Sarah, really really helpful article. What is your opinion about Pea Protein that have the lectins removed? Apex Energetics says that their pea protein is lectin free which leads me to believe it is safe. But maybe not? Would you distinguish between products like that? I have had many of my AIP clients on it with no issues, but I am not testing their gut antibodies while they are on it due to expense for them.

In some cultures, corn and beans are “the staple diet”. They are cooked in so many ways… I am also curious about lentils, garbanzo, etc. I know there are not many studies, but whenever you have any ideas, it would be interesting to know! Thank you for all you present to us.

Years ago, I read about the Paleo diet and wrote it off as too restrictive. Then went on to slowly eliminate foods from my diet one at time that made me feel like I’d been kicked in the gut after eating them. First gluten, then dairy, then rice, corn and all grains. Eventually, I found that psuedograins such as quinoa also gave me an immune reaction as well (sun rashes, interestingly). So instead of taking the advice of the Paleo diet, I did it in my own round about way, and came to nearly the same conclusion. After these eliminations by cystic acne cleared up, and my Hashimoto’s antibodies went from the thousands to around 8.

The thing is that I love chickpeas. They don’t seem to bother me at all. Still, I’ve always been curious about what would happen if I went 100% paleo and cut them out too. The problem is that I’ve since found that I’m histamine intolerant, so that cuts out all nightshades. It’s really frusterating. So far, everything that I have eliminated has been based on listening to my body. In the case of legumes, I would be eliminating based on advice instead of symptoms, and I hate watching my diet shrink like this. I feel the same way about eggs. Both of these foods make me feel pretty good. Would you recommend giving up foods that don’t seem to instigate symptoms? Or perhaps I’m just not aware of the symptoms they are producing. Every time I start thinking about making my diet even more difficult to manage, I sort of just shut down.

If you feel good with those foods, then I say go for it. There’s a great deal of individuality in terms of response to different foods and I thing honoring that by listening to your body is the most important thing

Enjoyed reading this post. Learned a lot. Was really impressed that you encouraged readers to listen to their own bodies when making food choices rather than insisting things be done one way.

Hi, I just wanted to say thanks for writing this piece. Great to find an article that gives a more detailed view on the specifics of lectins AND the wider context, this has given me much more perspective and makes sense. Warm regards, Steve

Hi Sarah! Just wanted to let you know that you did a great job.
I was studying for my Immunology class, reading about the mannose pathway of activating the complement syste, and started wondering whether anyone in the paleo community actually got into this stuff deeper, in a more scientific way. :)
And of course your website popped out, which I am not really surprised!
Anyway! Thanks for explaining it in a nice, clear way!
Hopefully when I graduate I will be able to do some benchwork to provide more evidence for primal diet!
Best,
Alex

Thanks for this very informative post :)
I’ve eliminated almost all forms of beans and grains from my diet since having a lot of digestive (and other) issues except for white rice which has always been a staple food where I come from! Does removing the bran from the rice reduces/removes the lectin? ie. is white rice safe? Thanks!

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