How Do Grains, Legumes and Dairy Cause a Leaky Gut? Part 1: Lectins

We make it clear that we are in no position to expertly and thoroughly explain the science behind the Paleo Diet. So many people, though, ask us about it. In response, we went out and found a scientist for you. Meet The Paleo Mom, a scientist-turned-at-home-mom. She has written a series of posts for us on the “why” of this way of eating. We hope this will be informative and fun for you. Check out her website, an adorable place full of interesting posts and cute drawings.

Part 2 of 4 in this guest series: How Do Grains, Legumes and Dairy Cause a Leaky Gut?  Part 1: Lectins

One of the fundamental principles of paleolithic nutrition is to protect the lining of the gut by eliminating foods that damage it.  By prioritizing gut health, we are able to treat and prevent the many health issues associated with having a “leaky gut”.  But how exactly do grains, legumes and dairy wreak so much havoc on the digestive tract?  There are several ways in which these foods create holes in the gut lining.  The best understood is the damage caused by lectins.


Grains and legumes contain lectins. Lectins are a class of proteins found in many types of seeds (like wheat, oats, barley, rice, peanuts, soy, etc.) that are part of the plant’s natural defense mechanism.  A digested seed is not one that can grow a new plant.  To defend itself, the seed from these plants either deter predators (like us) from eating them by making us sick or resist digestion completely or both.  The grains and legumes that have become a part of the human diet since the Agricultural Revolution 10,000 years ago aren’t toxic enough to make most of us severely ill immediately after eating them (otherwise humans never would have domesticated them!).  Instead, their effects are more subtle and can take years to manifest as a life-threatening disease.  You may be wondering why other seeds (like the ones in berries or kiwi or bananas) are okay to eat.  These come from plants with a friendlier defense strategy:  we get to eat the delicious fruit encasing the seeds and then the seeds, which pass through our digestive tracts intact, get to be planted in rich manure.  How do you know the difference between a harmless seed and one that contains damaging lectins?  Here’s the rule:  if you can eat it raw, then it’s okay to eat.  If you have to cook it, it has damaging lectins.


Lectins are not broken down in the normal digestive process, both because the structure of these proteins are not compatible with our bodies’ digestive enzymes but also because the foods that contain these lectins also contain protease inhibitors (compounds that stop the enzymes from breaking down proteins; more on these in Part 2).  Lectins, which remain largely intact throughout the digestive tract, can damage the gut lining in several ways.  First, lectins trick the enterocytes (the cells that line the gut) into thinking they are simple sugars.  The enterocytes “willingly” transport the lectins from the “inside-the-gut” side of the cell to the “outside-the-gut” side of the cell.  While in transit, the lectins may cause changes inside the enterocyte that either kill the cell or render it ineffective at its job, which leads to more pathogens leaking out of the gut.  Once outside the gut, these lectins activate the resident immune cells of the gut which respond by producing inflammatory cytokines (the chemical messengers that circulate in the blood and tell white blood cells to attack) and antibodies against these foreign proteins.  Because at least part of this response is not specific to the lectin itself, the enterocytes (being the closest innocent bystanders) can be targeted and killed by the body’s immune cells, leading to the microscopic holes that create a leaky gut.

Gluten is both the best known example of a lectin, and also the most damaging. In many individuals (like those with diagnosed gluten sensitivity and celiac disease), gluten can weaken the connections between enterocytes, essentially creating a space in between the cells through which gut contents can leak through, adding yet another way that this particular lectin can cause a leaky gut.  Once gluten has passed through the gut lining, it stimulates the resident immune cells of the gut to start producing antibodies.  Gluten is especially insidious because parts of this protein closely resemble many proteins in the human body, so there’s a high likelihood that some of the antibodies produced to target it will also target human cells.  One extremely commonly formed antibody is one against our enzyme transglutaminase.  Transglutaminase is an essential enzyme in every cell of the body, which makes important modifications to proteins as they are produced inside the cell.  It also stimulates wound healing, but if antibodies have formed against it, then when it is secreted by damaged cells in inflamed areas of the small intestine (or any other damaged tissue in the body), rather than helping to heal the surrounding tissue, it instead turns it into a target of the immune system.  This is yet another way in which gluten can cause a leaky gut.  Importantly, when antibodies against transglutaminase form, every cell and organ in the body becomes a potential target.  Because an exaggerated sensitivity to gluten is the cause of Celiac Disease, which affects at least 1 in 133 people, its effects on the gut have been the most studied.  Scientists still don’t know which of the many ways that gluten can harm the body apply to all lectins and which are specific to gluten.

Gluten sensitivity has already been linked to dozens of autoimmune diseases.  Even in individuals who do not have celiac disease or gluten sensitivity, it can take up to six months for the gut to fully heal after a single gluten exposure.  While other lectins may not be quite as damaging as gluten, scientists continue to discover new ways in which foods that contain lectins can contribute to a leaky gut, inflammation and autoimmune diseases.

About The Paleo Mom: Sarah Ballantyne is a scientist turned stay-at-home mom and a recent convert to paleolithic nutrition who is working hard to address her own health issues and to improve her family’s nutrition and health.  She blogs about her own experimentation with different implementations of the paleo diet, about her efforts to transition her family to paleolithic nutrition, and shares her successful recipes.  Sarah’s passion is to share her biology, physiology and nutrition knowledge through informative posts that distill the science behind the paleo diet into approachable explanations.  Visit her site at www.thepaleomom.com or on Facebook or Twitter.


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  • Tanya

    ( Here’s the rule:  if you can eat it raw, then it’s okay to eat.  If you have to cook it, it has damaging lectins.)

    So what does everyone think about green peas then? A legume, that is edible in it raw form? We always plant peas in our garden and the kids (who are naturally semi-paleo) snack on them when outside. What’s your opinion, do you think that because they have not matured and dried that essentially a green pea is still a baby that they have not developed any defenses? Just curious.

    Oh – great post by the way.

    • Protect me from the impending Paleo Police… but we let the kids grow and eat green beans, peas and corn when it’s in season at the Farmer’s Market or from our garden (yes, we grow corn).

      It depends on the state of your gut and where you are in your journey – I would never have a big bowl of split pea soup from a bag though! I’m particularly sensitive and anything in that “range” that’s been canned, bagged, etc. – WRECKS my tummy. Fresh corn or sprouted corn tortillas might give me some gas… but I survive. Just have to recognize it’s not ideal, IMO.

      Sarah will have WAY more science and a better formulated response I’m sure 🙂

      • Tanya

         Ha! Paleo police…
        Yes we grow everything too – and for the same reasons,it doesn’t bother anyone that I’m aware of. I’ve always had a garden even before we had kids, so we rarely ever have canned vegetables. I was feeling guilty last fall doing the peas and corn – both of which are huge hits in our house.  And it’s great fun to play hide and seek in the corn patch. Maybe I won’t feel guilty this year then because I doesn’t even seem to give anyone gas.

        Speaking of gas (ahem..) I made some beans the other day because I really wanted to try Spunky’s vanilla bean cake. Well omg – I ate some of the cooked beans while cooling, made the cake – had a little slice and not to long after I felt like I was going to explode or was miraculously in labor. So ah…. no beans for me I guess.

        p/s My ELaD book is in WV – yay! should be here next week. Can’t wait – you guys have had some really great reviews.

        •  Once on a trip we went to a grain-free vegan bakery only to discover too late that they used chickpea flour. The rest of the trip was painful and no fun!

          Hope you love ELaD!

        • powerfocus7

          I know what you mean…..they say if you do it beans you need to soak them for at least 24hours for me the next time I eat them I am thinking about soaking them for longer.

  • Cassie

    I posted this on Facebook already but these things may not cause damage to a person who is eating them traditionally prepared. But they would cause damage to someone who has been eating processed grains and dairy. But there are societies found by Weston a price who have been drinking raw milk and eating traditional sour dough and been extremely healthy.
    I think the main issue is if you are starting with poor gut health and further damaging it then that can cause numourous problems. But if you can fix and repair your gut you could eat traditional foods and be ok. Have you read Gut and Psychology Syndrome? It talks about healing a damaged gut and the author cured her daughter of autism. It’s a very enlightening book. I found that it answered a lot of the questions about my paleo diet.

  • OK but you can eat peanuts raw, right? Why are they banned?

    •  Sarah may have more to say, but essentially peanuts are not nuts, but beans. They grow in plants instead of trees and are in pods. So peanuts, like all legumes, contain the same harmful lectins as all beans and grains do.

  • Meso-Man

    Hey Paelo Mom – Fascinating stuff.

    Although, as you used to be a scientist, you should know that what would make this article a hundred times better is links to studies which have been peer-reviewed and published in a reputable journal. Otherwise you’re just another crank on the internet.

    • ThePaleoMom

      You are right. I wrote this article before I got in the habit of always including citations in my posts (which i do now). At some point, I will go back and add citations to this one. In the meantime, The Paleo Answer provides much of the same information with thousands of citations. You might also enjoy perusing PubMed.

  • Thank you for this explanation in more simple terms! Understanding helps me to stick with my diet!

  • Ann

    I know you are trying to help Matthew…..but you are soooooo wrong on your statement that says ( here’s the rule if you can eat it raw then it’s ok) I know because I have a bad reaction to most lectins and I am on a very limited diet. So eating things like strawberries, blackberries, apples peanuts raw garden peas salad items such as radish cucumber (but only the seeds the flesh is ok) Tomato’s ( which is one of the biggest offenders, as it is part of the nightshade family) just to name a few! which have lectins and causes me to be ill or in pain with fibromyalgia. If I don’t eat foods with lectins then I don’t have the fibromyalgia.
    If anyone thinks that they have a problem with lectins, then please do your research to which foods have them and which don’t. stay on that diet for 3 weeks and when you are feeling better in yourself then start to introduce food items that have lectins one at a time and see if you react to it. If you do then leave it out of your diet.
    Hope it helps anyone looking for answers!

    • This was actually written by Dr. Sarah Ballantyne, Matthew just posted it. Her doctorate in scientific research is the basis for this article. That said, we always encourage everyone to listen to their bodies…

      Above confirms the most offending list of lectins, in alignment with Sarah’s post.

      • Ann

        Thank you for that….I have now read Dr Sarah Ballantyne article and I have got some helpful info from it. However she must have taken the above rule out as I could not find it.

        There is a paragraph though that does state the toxicity of fresh foods, as below…..

        Nachbar and Oppenheim (1980) found 30% of fresh and PROCESSED foods contained active lectins. Lectins from green salads, fruits, spices, seeds, dry cereals and nuts (even after roasting) showed activity of potentially toxic lectins.

        What I would like to know…if you can help is that I also have a underactive thyroid which could be due to the lectins. If it is and I can leave out the offending lectins will it rectify it’s self or would the damage be permanent? I have not been able to find anything on the subject.

        • dR JOSH AXE HAS MANY INFORMATIVE VIDEOS..check him out