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Though ‘toxic,’ with proper preparation lectins can provide great nutrition

I remember it distinctly. Three years ago I received a lot of questions regarding a certain doctor’s book (and his numerous YouTube ads) regarding a certain food “toxic” substance present in “healthy” foods.
The substance was labeled as highly toxic and the instigator of most of our modern chronic diseases. The kicker was, all these foods that contained this nefarious substance were supposed to be healthy for us.
The substance in question? Lectins.
I sort of thought the issue had decreased in popularity. That is, until I recently saw a slew of ads by the same doctor, again on YouTube. I’ve decided to revisit the subject.
What exactly are lectins, where they are found, what effect do they have on us and what should our response be?
Lectins are a class of proteins that bind carbohydrates. The name Lectin actually indicates their function since lectin means to gather, select or combine. Yes, lectins’ primary function is to select, bind and combine specific carbohydrates. They can be found to some degree in most of plant foods: nuts, seeds, nightshades (tomatoes and potatoes), beans (including green beans), legumes and grains. There are some lectins found in animal products too. Basically, they are everywhere but in a higher concentration in plant foods.
The carbohydrate-binding action of plant lectins is actually incredibly useful to plants and in medicine. Lectins in plants act as protection from fungus, bacteria and animal predators by making the plant resistant to digestion and destruction. This is one primary reason why animals are great seed scatterers.
Since the dry, raw seeds and nuts they eat are resistant to digestion, they pass on in their excrement to become “planted” elsewhere. It’s an intended design.Lectins also transport carbohydrates in the plant, recognize pollen and aid in maintaining seed dormancy, in addition to so much more.
In the field of medicine, the ability lectins have to bind specific carbohydrates makes them useful in blood-typing, immunological studies, mapping of neuropathways, and cancer treatment, just to name a few.
So what does all this selecting and binding capacity mean for humans who eat these plants? Are they really toxic to humans? In short, yes.
What makes lectins “toxic” to humans has to do with their resistance to digestion, their effect on digestive enzymes, the changes they make to the gut wall and gut bacteria as well as their ability to travel systemically throughout the body.
Lectins’ protein structure is incredibly robust. They cannot be broken down by our stomach acid or by our digestive enzymes in the small intestines. But not only do they refuse to be digested themselves, they inhibit the digestion of other carbohydrates and proteins by binding to the digestive enzymes (the chemicals that your body creates to break down what you eat).
Once bound to lectins, your digestive enzymes cannot break down and absorb some of the nutrients from food. Additionally, lectins affect your ability to digest food by altering the structure of the gut lining. By flattening these structures, once again, your ability to absorb nutrients is diminished. Lectins also seem to create an environment more suitable to bacteria such as E coli (which is pathogenic if present in too high amounts).
The effects of lectins can become systemic (body-wide) too. They pass from the gut into the bloodstream where they are circulated and have been found deposited in blood and lymphatic vessels. Research has also shown that lectins may trigger a degree of inflammatory response from your immune response as well.
While the effects listed above are more subtle and chronic, it should be noted that the toxic effects of lectins from uncooked or undercooked beans and pulses can be very acute as well. The immediate symptoms include nausea, vomiting and diarrhea. The body obviously recognizes that it has ingested a threat and attempts to expel it.
One thing to note is that the scholarly journals I’ve researched do not indicate the exact amount of lectins needed to exert toxic effects in humans.
Much of the research has been derived from animal studies. Presumably, the dosage of lectins producing toxic effects in lab rats would be different in humans. So we know that the effects of lectins are toxic to humans; however, it is unclear how much.
As is typical with toxins though, we know there will be some sort of threshold.
Regardless, the picture seems a bit ominous. The wholesome nuts, beans, seeds and grains that have been touted as oh-so-nutritious would appear deleterious to our health. This would certainly be the case if it were not for appropriate food preparation and processing.
A study published in March of 2018 showed that soaking soybeans and pulses (chickpeas, peas, fava beans, beans, and lentils) reduced the lectin content by 1 to 5%. Further cooking for one hour at 203F reduced the lectin content by 96 to 99%! Basically, lectins could be removed almost entirely!
So while lectins are resistant to an individuals’ digestive process, soaking and heat appear to render them harmless, at least for beans and some grains. It should be noted that some studies have indicated that slow-cooker temperatures may not be high enough to do the job and that temperatures greater than 176F should be used for at least 10 minutes (although I believe many brands do. You can check your user manual). This is where the pressure cooker comes in extremely handy.
Vegetarians, vegans and “raw foodists” should take a special note to this, as their intake of lectin-containing foods is likely very high. If they do not prepare these foods appropriately, they are at risk of malabsorbing many essential nutrients and potentially causing inflammation in the gut.
So, are lectin-containing foods safe to eat or should they be eliminated completely? My professional opinion after doing the research is that yes, many of these foods are safe and wholesome when prepared correctly. Beans, legumes and even grains should be soaked and cooked at a high temp.
Nuts and seeds and are also best soaked. Unfortunately, my research did not extend to some of the commonly eaten raw veggies like tomatoes that also include lectins. Does cooking disable those lectins? Unfortunately, I still have no answer as of yet. (A topic for a future article perhaps?)
As with anything, there are cautions and exceptions. For individual with digestive issues, (allergies, bloating, diarrhea, or chronic constipation, etc.) then yes, some raw, high-lectin foods may bother them. Might individuals be sensitive to them even after appropriate preparation and cooking?
It is possible. Individuals with autoimmunity, compromised gut function, a hypersensitive immune system, and chronic inflammation may not find lectins helpful or tolerable. Their bodies are simply not in a place to process lectin-containing foods in a functional way. But to say that that no one should eat foods containing lectins, is probably a misguided interpretation of the research at best and a trouble-making one at worst.
In the end, consumers should be both confident and discerning. Be confident that certain diverse and abundant lectin-containing foods can be health-promoting when soaked and cooked. They offer fiber, phytochemicals, antioxidants, and low glycemic properties that can moderate appetite, lower cholesterol, blood pressure and blood sugar and fight inflammation and cancer.
But also be discerning of your own body’s response to lectin-containing foods, the methods used to prepare them, and the amounts tolerated.
As may be evident here, sometimes the answers to nutrition questions are not straight-forward. It is good to keep asking and to apply the information as discernment and a person’s individual needs allows.

– Cathryn Arndt is a Registered Dietitian Nutritionist (RDN) who operates a nutrition counseling business called The Pantry Lab LLC. She lives in the Lebanon area with her husband and daughters. For more information or to comment, contact her at thepantrylab.com or visit her Facebook page by searching for Dietitian Cathryn.