Why Grains Are Bad–Part 1, Lectins and the Gut

November 28, 2011 in Categories: , , by

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The idea that grains are harmful is one of the most fundamental tenets of the Paleo diet. But, the rationale for avoiding them is often misunderstood, and sometimes oversimplified to the idea that early humans didn’t have access to significant quantities of grains, and therefore, we shouldn’t eat them either (an argument that’s hardly scientific and extremely easy to refute!).

Actually, a large body of literature (as well as basic physiology and biochemistry) sheds light on how grains can harm us, and why replacing them with nutrient-dense Paleo foods can be a boon for our health. Here’s what we need to know!

Grains have a particularly high concentration of two types of lectin. Lectins are a class of proteins that are present in all plant life to some degree (the gluten in wheat is a famous example). Two sub-classes of lectins, prolamins (like gluten) and agglutinins (like wheat germ agglutinin) are of particular concern for human health (see also Are all lectins bad? (and what are lectins, anyway?)). These “toxic” lectins are part of a plant’s natural defense system against predators and pests, and are usually concentrated in the seeds of the plant (which is why grains and legumes have so much). 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.

So, what happens when we eat consume these prolamins and agglutinins? Similar to what occurs in individuals with celiac disease (basically, a super exaggerated form of the sensitivity we all have to gluten and other lectins), these particular lectins can either damage and kill the cells that line our intestines, or directly cause spaces to open up between our gut cells. Yikes!

First, these types of 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 and also because the foods that contain these particular lectins also contain protease inhibitors (compounds that stop the enzymes from breaking down proteins). These lectins can 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 “toxic” 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.

Gluten causes a leaky gut

The many mechanisms that we know gliadin fragments (fragments of partially digested gluten) can enter the body, harm the gut barrier, and stimulate the immune system.


Once outside the gut, prolamins and agglutinins 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) as well as 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.

The result is what essentially amounts to tiny holes in our intestines, allowing the entrance of things that are not supposed to get into our blood stream. This “leak” is made worse by the fact that lectins bind to sugars and other molecules in the gut, in turn “helping” these random other molecules leak into the blood stream. There are many things in our guts (like the bacteria E. coli) that are supposed to stay there; and, when they enter into the blood stream, they cause a low level of systemic inflammation. This can set the stage for many health conditions, including cardiovascular and autoimmune diseases.

A huge number of prolamins and agglutinins exist in food, and some are more harmful than others. Gluten is by far 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 escape, 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 commonly formed antibody triggered by gluten exposure is against the enzyme, transglutaminase. Transglutaminase is an essential enzyme in every cell of the body. It makes important modifications to proteins as they are produced inside the cell, and also stimulates wound healing. But, the playing field changes if antibodies have formed against it! When damaged cells secrete transglutaminase 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 the area into a target for the immune system. This is yet another mechanism linking gluten with 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.

But, non-gluten lectins can be harmful as well. Wheat germ agglutinin may actually have a larger negative impact on our health (it has the added effect of stimulating inflammation), which is why the simple act of removing wheat from our diets can make such a profound difference. And, while some of the other “blacklisted” foods are okay for occasional consumption (like dairy, beans, and rice), I suggest a lifelong dedication to gluten and wheat avoidance. It can take up to six months for our guts to fully heal after a single gluten exposure (see How Long Does it Take the Gut to Repair after Gluten Exposure?)!

Beyond the fact that some lectins are more problematic than others, dose is another important factor here. The vegetables and fruits that our prehistoric ancestors ate in large quantities are generally very low in lectins, and come 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. (That’s much different than the case with grains, whose lives depend on not getting eaten and crushed with our teeth!) And, the lectins fruits and vegetables do contain generally interact much less strongly with the gut barrier than the lectins found in grains. Grains (especially wheat) and legumes (especially soy and peanuts) are very high in prolamins and agglutinins, the two sub-classes of lectins with the greatest negative impact on the barrier function of the gut. (That’s where the gut is supposed to selectively allow digested nutrients from our foods into our body and keep out everything else.) And, if damaging the gut lining and causing systemic inflammation isn’t enough, lectins are also anti-nutrients, which means they stop us from absorbing many of the vitamins and minerals in our food (like calcium!). Given that they’re also a nutrient-poor food choice (see Gluten-Free Diets Can Be Healthy for Kids and Why Grains Are Bad: Part 3, Nutrient Density and Acidity), the cons list is really stacking up!

With all that in mind, it’s easy to see why grains aren’t a good food to include in our diet (much less eat as a staple!). But, the problems with grains don’t end with lectins. In the next installments of this series Why Grains Are Bad–Part 2, Omega 3 vs. 6 Fats, and Why Grains Are Bad: Part 3, Nutrient Density and Acidity, we’ll learn more about how grains can harm our health at a biochemical level!

why grains are bad part1


Agardh D, et al. “Reduction of tissue transglutaminase autoantibody levels by gluten-free diet is associated with changes in subsets of peripheral blood lymphocytes in children with newly diagnosed coeliac disease.” Clin Exp Immunol. 2006;144(1):67-75.

Alaedini A & Latov N. “Transglutaminase-independent binding of gliadin to intestinal brush border membrane and GM1 ganglioside.” J Neuroimmunol. 2006;177(1-2):167-72.

Antvorskov JC, et al. “Dietary gluten alters the balance of pro-inflammatory and anti-inflammatory cytokines in T cells of BALB/c mice.” Immunology. 2013;138(1)23-33.

Antvorskov JC, et al. “Impact of dietary gluten on regulatory T cells and Th17 cells in BALB/c mice.” PLoS One. 2012;7(3):e33315.

Calder PC. “Omega-3 polyunsaturated fatty acids and inflammatory processes: nutrition or pharmacology?” Br J Clin Pharmacol. 2013 Mar;75(3):645-62.

Dawson-Hughes B, et al. “Alkaline diets favor lean tissue mass in older adults.” Am J Clin Nutr. 2008 Mar;87(3):662-5.

De Punder K & Pruimboom L. “The Dietary Intake of Wheat and other Cereal Grains and Their Role in Inflammation.” Nutrients. 2013;5(3):771-787.

Scialla JJ & Anderson C. “Dietary acid load: A novel nutritional target in chronic kidney disease?” Adv Chronic Kidney Dis. 2013 Mar;20(2):141-149.

Simopoulos AP. “The importance of the ratio of omega-6/omega-3 essential fatty acids.” Biomed Pharmacother. 2002 Oct;56(8):365-79.

Vasconcelos IM & Oliveira JT. “Antinutritional properties of plant lectins.” Toxicon. 2004 Sep 15;44(4):385-403.

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I love this! Thank you so much for the explaination. I am transitioning to the paleo diet myself and the knowledge of what grains do to my body is making the change feel like its saving my life instead of depriving me. Thank you!!!

What about sprouted grains? I honestly don’t know much about them but have heard really really good things. Once a grain has “sprouted,” is it paleo friendly? Thanks!

Hey I too would like to know if sprouted grains are okay, or at least semi-okay! I know they’re okay in weston price’s view…and for those of us who struggle to keep weight on it seems a good option..

All grains and grain products should be eliminated for 30-90 days. You are welcome to try reintroducing sprouted grains if you would like to see how you tolerate them at that point. – Christina, Sarah’s assistant

Out of curiosity, have you ever read Mat Lalonde’s criticisms of the paleo diet? He has some good points. You wrote a good article. I was just wondering what you thought of him. thanks

I super respect Mat Lalonde. I think many of his criticisms are outstanding points and some are an overstatement in the other direction. My article (Re)defining paleo is in part inspired by some of his points from his Organic Chemists Point Of View of Paleo lecture.


do you have any research articles or established scientific sources to support these claims? I just want to be sure and learn more.


Corn grits? And organic? I think the real question to answer is how you feel you do with them. We have organic locally-grown pop corn as an occasional treat in our home and we all seem to tolerate it well.

Could you please post the journal articles that you got your information from? I would love to read the solid science that backs this up to support this claim.

I am 58 and just found out I’m borderline diabetic and I’m slim enough to control it via diet. No milk, butter ok.(A little milk in the morning coffee is ok) But I cut out the grains also (which I used to crave) EXCEPT swedish krispbread (knackebrod). Knackebrod is flat, hard, yeast free and is ALL rye. Rye naturally has no gluten. My dad had that when we were kids, I grew up on it and he lived to be 90. It is a staple in Scandinavian countries in lieu of bread. And they have many healthy people there if they stay away from the Mickey D’s.

phosudo science bull shit . Sorry kids.. it true crap.. fact is ANY whole food is ok . Give your collective heads a shake and MAYBE embrace some common sense ( just for a change)

Further more, this type of garbage advice has led to an epidemic of “peanut” allergies and a host of other ” allergies” previously unheard of. All thanks to half truths like this contained in this web site and related web-sites. Follow this: eat less , move more. Cut out man made processed garbage and ” food like” products.. Do this and you and your children will be fine. EVERYTHING else is a book designed to separate you from your money and has NOTING to do with your health , your well-being, or anything that remotely resembles common sense.

It’s hard to know if any of this has any validity without proper citations, it is true, but you fail to cite anything as well.

I sure wish people would stop claiming they have scientific evidence of anything without citing some actual research.

Peanut allergies (and auto-immunity) are on the rise due to vaccinations (peanut oil in them…grown on human DNA or foreign animal proteins). but i agree with you on the whole food WAP idea. i’m using AIP for a short-term healing diet to find out what i do react to only.

Keep in mind how our brains work. It doesn’t matter if its a quantum physicist, Medical Doctor, nutritionist, teacher, fireman, soldier, governor, male, female, or soccer Mom. Our brains don’t like change! It takes a while to accept and believe new information. Science is a great way to change our beliefs, but testing it yourself is usually better. I tried it, and it worked for me. It gave me a (90% subjective) arthritis pain reduction, even though I thought it wouldn’t, it did. It seems to work even if your brain doesn’t want you to believe it does. After 8 months I’m beginning to believe.

Friends, I have been transforming my diet for the past 20 years; however, I still ate the grains and legumes, and was still quite sick, and specially gut swollen after meals. Six months ago, I totally eliminated all wheat products, grains, sugars, legumes. Apart from the fact that lost 10 pounds and I’m now at 100 lbs, I have to gut problems anymore, I can eat just about anything, but most of all, my health is the best. My daughters told me this month: Mom, this is the best health you have ever had in your life. I had half a cup of “whole wheat” in the house I was invited to celebrate mother’s day, and all my joints were swollen by Monday morning, and I DO NOT have arthritis. When your body is desintoxicated, you feel it right away. So, friend, do not complain if you have not dared to try a healthier lifestyle, and are still complaining about your lousy health. This is a 65 year old that can now do 40 yr old exercises, feel better than ever, and the energy is on woman high all the time! YEAH!

Great info, after suffering serverly with no answers finally concluded dairy protien was making me very ill. Now skin problems I suspect are caused by tomatoes. Good info keep up your information. If readers are skeptical then they are probably lucky enough to be able to tollerate these foids, but I dont appreciate their attitudes towards your ideas. Good job.

I wondered if there was any evidence that fermented grains (such as in homemade sourdough starters) would still contain these harmful lectins/other damaging substances?

[…] The Paleo Mom has a brilliant article on Anti-nutrients that covers a bit more in depth science behind it all: “Grains have a particularly high concentration of two types of lectin. Lectins are a class of proteins (of which gluten is one) that are present in all plant life to some degree. Two sub-classes of lectins, prolamins (like gluten) and agglutinins (like wheat germ agglutinin) are of particular concern for human health. These lectins are part of a plant’s natural protective mechanism (from predators and pests) and are usually concentrated in the seeds of the plant (which is why grains and legumes have so much). So what happens when we eat these proteins? Similar to what occurs in individuals with celiac disease (basically, a super exaggerated form of the sensitivity we all have to gluten and other lectins), these lectins can either damage and kill the cells that line your intestines or directly causes spaces to open up between your gut cells. This causes little holes in your intestines; so, things that are not supposed to get into your blood stream leak out. This “leak” is made worse by the fact that lectins bind to sugars and other molecules in the gut and then “help” these random other molecule leak into the blood stream. There are many things in your gut (like E. coli) that are supposed to stay there; and, when they leak into the blood stream, they cause a low level of systemic inflammation. This can set the stage for many health conditions, including cardiovascular and auto-immune diseases.” […]

When we started farming for the first time, we farmed grains. Grains are part of the reason we are here today, how can you explain this paleomum?
If we all actually had gluten issues we wouldnt have gotten past farming and wouldnt devloped society as such. How can grains be a core part of our evolution and be bad?

So I followed SCD for about 3-4 years and have greatly slipped on my eating since then. As a fellow scientist this speak VOLUMES to me. Thank you for scaring me 😛 No more grains for me. I need to take quotes from this and post it at my desk and in my kitchen so remind me 🙂 Thank you <3

[…] there are however other aspects which are worth taking into account. By regarding gluten simply as aggressive to our interior gut lining, it may very much overlap with other aggressive proteins such as phytic acid or lectins which are […]

Thank you ! I need to know if brown or white rice contains lentics. We eat rice every day! I think if you cook very well the grains ,those lentics disappear. It is too difficult to eat without grains, then what are we going to eat ??? When I cook beans I put them in a bowl of water with a one teaspoon of pure baking soda, all night, the BS. is suppose to take away every thing and also make the beans softer, in the morning you cook them in a crockpot or wherever. Also, the BS. is alkalizing….

Rice does contain lectins. Cooking reduces the lectin content slightly, but soaking/sprouting the grains will reduce it further. White rice is more easily digested than brown rice and can be a good option for some. Some people tolerate soaked/sprouted and cooked grains and legumes, but others do better avoiding grains and legumes altogether because of all the reasons listed in the article. There are plenty of other foods out there to eat when you’re not eating grains, namely lots and lots of veggies. -Kiersten

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