What are lectins? Do lectins cause disease? Discover all now

“What are lectins” is the recurring question in recent years among health-conscious people.
This does not come as a surprise to those in the industry, since for several years now the tabloid media and fad diets/dietologists have been pointing to lectins as the main cause of obesity, chronic inflammation and autoimmune diseases (who offers more?): and this misinformation is particularly serious, because as you will read in a moment, lectins are mainly present in foods that have always been considered healthier, especially those of plant origin!
Given the growing interest in a diet rich in plant-based foods (even in the United States, some 33% of the population claims to eat less meat[1]); and given also that CHE Food Revolution has been at the forefront of promoting this change for several years now, I feel it is my moral duty to shed light on this paradoxical issue.

I will answer the question in this article, analyzing also various related topics in detail:

– What are lectins?
– How many types of lectins exist?
– Which foods they are found in?
– Do lectins cause disease?
– Benefits of lectins and foods containing them;
– How to eliminate lectins or reduce their concentration in food in a healthy way?
– Conclusions

What are lectins and their main characteristics

Lectins are part of a diverse group of protein families, which have in common the ability to recognize and bind in a reversible and specific manner to certain carbohydrates: in particular mono and oligosaccharides (or mainly sugars if you prefer).
They are abundant in nature and present in all living organisms: from viruses to humans. This is why lectins can be found in almost all foods such as cereals, fruit, vegetables, fish, meat and meat products, albeit in different quantities.

In addition to their ubiquity, another important peculiarity of lectins is that although they are proteins (normally above 60°C they begin to denature, and generally above 80°C all proteins denature: but as we will see below, it takes more than that to alter the structure of lectins of plant origin), they are very stable, heat-resistant molecules.
Likewise, not even stomach acidity or digestive enzymes can effectively break them down; and that is why they are able to reach the intestine unaltered, where some, if left untreated, can cause health problems.
What appears to be a spite towards the human being (yes, we humans have a tendency to see ourselves as the center of the universe), is actually nothing more than a sublime way of the plant kingdom to defend itself against invaders, constituting the only weapon of survival, developed over millennia of evolution.

Lectins, due to their ubiquity and precious biological value, can be compared to enzymes.
This is why, for more than 130 years (i.e. since they were discovered), various studies and scientific research have been trying to shed light on their characteristics, with the aim of achieving improvements in various branches of science and technology: agriculture, medicine, bio-medicine, biology, oncology, immunology, glycobiology, genetic engineering,… [2,3].

In this article, for obvious reasons of space and relevance, I will only analyze dietary lectins.

Another really fundamental feature is that despite classifying them under the same name, there are actually a myriad of lectins, each with different peculiarities. And we will see why this is one of the crucial aspects: there is lectin and lectin!

How many types of lectins exist?

The main classification of lectin families is based on their amino acid sequences, structures and properties[4].

In addition, there are models that divide plant lectins into 12 distinct families, depending on their carbohydrate-binding domain (the sector where they bind).
But believe me, it is definitely irrelevant to know the names of all the families; besides making your eyelids heavy, these classifications are constantly being updated, following the development of science and technology, which makes the previously absorbed information (probably) useless.
We therefore devote our attention to the most famous lectins, among more than 500 discovered so far:

One of the best known of the entire category is undoubtedly the haemaglutinin or phytohemagglutinin (PHA)[5].
They are part of our food chain to a considerable extent: I refer to the large family of legumes, which have been used by all populations for millennia.
Although some lectins belonging to this category, when in active form, can cause agglutination of erythrocytes (i.e. red blood cells)[6], not all legumes are equally dangerous.

The most famous and certainly most fearsome is the red kidney bean, which boasts three times the amount of PHA present in white beans[7,8].

Then we have soya bean agglutinin (SBA), peanut agglutinin (PNA), lentil agglutinin (LcA), pea agglutinin (PsA).

In addition to legumes, other very common vegetables are also part of the group: garlic agglutinin (ASA), banana agglutinin (Mus a 2) and in particular perhaps the only ‘real rival’ to the lectins of legumes (PHA), namely wheat lectins (WGA).
Wheat lectins are more technically referred to as wheat germ agglutinin (WGA): the wheat germ guards the survival of the species, and is the most protected area of the entire grain; consequently, it contains high amounts of lectins.
Although wheat germ agglutinin (WGA), when active (I will explain these later), is toxic to mammalian cells in culture (in the laboratory) and to animals, its toxicity is still at least 1000 times less than that of ricin (Ricinus communis L.), arguably the most treacherous and macabre lectin, historically speaking[9] – I refer to the use of castor oil.

Important point: toxicity tests are carried out by bombarding human cells isolated in vitro with lectins in active form and in exaggerated quantities; the same thing, unfortunately, happens with animal testing.
You well understand that such tests do not make much sense, as they do not apply to the normal routine, one of which is the intake of lectins in active form: you will soon understand what I mean.
As well as many other aspects that we could talk about for hours.

Which foods contain lectins?

Although, as mentioned earlier, lectins are proteins found in all foods (fruit, vegetables, cereals, pulses, tubers, animal products, fish), the ones of greatest concern with regard to nutrition, are purely of plant origin.
In essence, it is believed that a good 30% of the foods that make up our diet contain high doses of lectins: legumes, cereals and oil-seeds above all. Specifically, lectins account for 0.1-5% of the total protein in dried legumes: that is, a considerable percentage.
Lectin-rich foods are red kidney beans, peanuts, soya, elderberries, garlic, peas, lentils, broad beans, barley, rice, rye, wheat, potatoes, leeks, onion, etc.

Do lectins cause diseas or not?

Having seen what they are, how many types and where they are found, we now look at whether lectins are really bad for you and why.
It seems that ingesting 5-6 red kidney beans raw or not properly cooked can lead to serious poisoning or even in some cases be fatal.
Apart from the specificity of this ‘singular’ legume, normally the consumption of foods containing high amounts of lectins, if in active form, i.e. without any pre-treatment and in large quantities, can cause simple discomfort, such as bloating, diarrhea, indigestion, allergies, etc.; the extent of these symptoms can worsen particularly in people with chronic disorders of the gastrointestinal tract: Crohn’s disease, permeable bowel syndrome, etc.
All right, but why?
I have already mentioned that lectins are very, very stable and resistant proteins. In other words, the work of our digestive enzymes is ineffective for a large part of the lectins ingested in an active form; just as the action of low pH stomach acids is ineffective. For these reasons, lectins (somewhat like chitins) manage to pass undisturbed through the digestive tract, retaining their active form.

READ MORE ABOUT CHITINS AND THEIR EFFECTS ON THE HUMAN BODY HERE

Normally, when (almost) digested food passes through the intestine, the wall of the intestinal mucosa allows the passage of nutrients through specific small openings; in this way, the assimilation of what the body needs takes place.
While nutrients pass through these openings, the intestinal wall continues to act as a barrier to unwanted substances and/or microorganisms: viruses, pathogenic bacteria, and so on. If the intestinal wall is already compromised due to the previously mentioned diseases, the active lectins in food can worsen the condition.

To better explain how, I will have to get a little more technical.
The surface of the intestinal villi is covered by a kind of sugar shell (glycocalyx); as lectins are selective towards sugars, they are attracted to this shell, anchoring themselves on the epithelium, together with other glycoproteins and glycolipids; here, possibly triggering a series of complex mechanisms, they can alter the structure of the villi, flattening them (or if you prefer, atrophying them), they can cause an enlargement of the openings (those predisposed for nutrients) on the epithelial surface of the intestine, and they can adversely affect gastric secretion necessary for nutrient absorption.

In addition to this, decreased absorption also occurs due to the reduction of intestinal surface area caused by the atrophied villi.

This is why lectins are said to adversely affect the absorption of essential minerals, such as calcium, iron, phosphorous, zinc, and protein [7,11,12], leading to nutrient deficiencies and weight loss.

Another problem attributable to lectins is the body’s reduced ability to defend itself: if the protective role of the barrier is lacking, the door could open wide for unwanted substances and microorganisms; presumably leading to inflammation and various problems with the immune system[13].
On the basis of these theories, some fad diet gurus, including famous doctors, claim that ‘all lectins are harmful and for all people‘; it follows that, according to them, ‘all foods containing lectins should be eliminated from the diet or their consumption drastically reduced‘.
According to these now-millionaire so-called experts, ‘ingesting lectins will, in the long run, cause permeable bowel syndrome, obesity, chronic inflammation, rheumatoid arthritis, cardiovascular and autoimmune diseases‘; even to those who have no chronic gastrointestinal system diseases.
And so the absurd lectin-free diets were born: dietary plans that remove most lectin-containing foods from the diet; at the same time, however, they involve massive use of expensive enzymes and supplements (in order to digest the remaining lectins and/or counteract any damage caused)!

You’ve probably been a little scared up to this point; after all, all this is destabilizing, and if you think about it, that’s the way it should be… or rather, it is functional in order to cash in on diets, consultations, books or miraculous packages of enzymes and supplements.
Except that the circus is based on an exaggeration!
And our good fortune is that we have chosen to eat consciously, avoiding falling into the many traps: ‘at the moment there is no scientific evidence to prove a correlation between lectins and the aforementioned diseases‘. While it is true that more and more people are suffering from diseases that have been identified as rare in the past, the reason for this must be sought in our other errors; because the overwhelming majority of the world’s population continues to consume lectin-rich foods without any problems.
In any case, let us proceed with scientific rigor and analyze the subject in more detail with the current knowledge available to us.

Why lectins are actually not bad (for everyone)

In principle, lectins are not bad for healthy people.
I state this without hesitation, because to date (11.12.2022) after some 130 years of the history of Lectinology, there is no scientific evidence on living people (in vivo), which can confirm without a shadow of a doubt, the correlation between certain diseases and the ingestion of lectins; nor even an established full recovery after the elimination of lectin-containing foods from the diet[14,15,16,17].

Let me be even clearer: despite numerous alarming claims about it, no scientific evidence tells us that eliminating lectins in food will cure 100% of ailments or medical conditions, including autoimmune diseases.
On the contrary, there is an obvious reflection, which is scientifically certain: to cause certain damage, ingested lectins would have to be biologically active, i.e. capable of preserving their ability to bind to carbohydrates, i.e. sugars; practically speaking, foods containing lectins, such as legumes or wheat, cannot harm you (if you are not predisposed) simply because we are not in the habit of eating them raw!
Of course, no one can put their hand on the fire and perhaps in the near future we may have more scientific results on their dangerousness; but while we ‘wait for Godot’, we can rely on the evidence of the past: the centenarians examined by the famous ‘Blue Zone’ study residing in certain specific areas of the world (Ogliastra in Sardinia, Okinawa in Japan, Nicoya in Costa Rica, Icaria in Greece and Loma Linda in California), all led, without exception, a diet based on foods rich in lectins and very little animal protein; in fact, they lived happily, healthy and long.
But it must be said that well before this study, we were aware of the benefits of the real Mediterranean diet, thanks to Ancel Keys: the first to associate a healthy cardiovascular system with a diet based on grains, legumes, vegetables and few animal products[18].

The benefits of lectins and foods containing them

Despite the recent crusade against the cause of all ills, which we have now realized is the result of economic interests, lectins actually have several antioxidant[19], anti-cancer[20,21] and antimicrobial[22,23] properties.
This is why lectins derived from plants and animals are commonly used to directly combat pathogens and for immune regulation[24,25].
In spite of accusations as the cause of obesity, lectins demonstrate characteristics that can be associated with the modulation of blood glucose[26].

In addition, it is worth mentioning that while the dangerousness of lectins has not yet been demonstrated in human models (I explained at the outset the enormous importance of this detail and the misleading experiments), the scientific literature is replete with clinical trials confirming the relationship between diets rich in legumes and whole grains, and reduced inflammatory biomarkers.

Again, a 2013 meta-analysis informs us that a high intake of whole grains, but not refined grains, is associated with a reduced risk of type 2 diabetes: results in line with the recommendations of various health institutions; i.e. replacing refined grains with whole grains, consuming at least two portions per day, in order to reduce the risk of type 2 diabetes and other metabolic disorders[27].

So, far from eliminating them from the diet! One must introduce lectin-rich foods without fear, considering that processing procedures reduce their concentration significantly.

How to inactivate them or how to reduce/eliminate lectins in food

We have said that lectins are not bad for you, provided you ingest them in their inactive form.

The surprising insight of popular knowledge has now also been proven by science: domestic processes developed to process certain lectin-rich foods are actually able to inactivate them; allowing us to enjoy their taste and nutrient content without risking any discomfort!
These processes include:
– soaking;
– repeated washing;
– cooking;
– fermentation;
– sprouting;

Repeated washing and soaking

By soaking and/or repeated washing, we can already reduce a good amount of lectins, as most lectins are water-soluble[28].
For proper efficiency, soaking must be prolonged (minimum 12 hours, changing the water at least twice).
Do not use the soaking water for cooking; if you wish to optimist water consumption, use it for watering the plants.

Cooking

Cooking or heat treatment not only makes food taste better, but also increases the absorbability of nutrients and considerably removes the remaining lectins.
It should be borne in mind that the majority of lectin intoxication injuries occur mainly from consuming lectin-rich raw food, or food that has not been cooked properly[29]; this is why cooking requires some strict rules.
The best method for reducing lectin concentration is to adopt wet, high-temperature cooking: boiling, stewing, preferably in a pressure cooker, as the latter allows us to exceed 110 degrees[30].

DISCOVER ALL PROS (AND CONS) OF THE PRESSURE COOKER HERE

However, the infamous PHA in red kidney beans shows remarkable resistance to heat.
Fans of slow cookers must be particularly careful, as slow cooking without boiling fails to interfere with the stability of PHA lectins: research even shows that slow cooking at 65 degrees for 12 hours was completely ineffective in denaturing them[31].

The FDA (US Food and Drug Administration) recommends soaking for at least 5 hours, followed by cooking for 30 minutes (at boiling temperature); while for the WHO soaking should last at least 12 hours, 10 min cooking at boiling temperature may be sufficient[32].

This is why I advise against adopting my beloved technique of passive cooking (with a blanket), especially for red kidney beans. As I explain in the article on pressure cookers, the most effective way to reduce lectin concentration is to cook pulses with high pressure, of course after a long soaking period and repeated washing.
The advice on using a pressure cooker becomes especially recommended for those living in high altitude areas, due to the lower boiling temperature.

Leavening/Fermentation

As just explained, high temperatures applied in a wet environment help to significantly reduce lectin concentrations.
But some foods, take bread for example, cannot be boiled!
So you have to stop eating it?
Don’t worry, if you have followed my advice on long-rising sourdough bread, there is nothing to fear: with this method, the lectin concentration is significantly reduced[33].
Generally, all types of fermentation/leavening help with this, as lectins are susceptible to the process; and it is because of this that several fermented legume and soy foods manage to be risk-free; even one study states that their concentration in soy and legume products, after fermentation processes, decreases by 95%[34].

Sprouting (Bioprocess)

As I explained in the guide on homemade sprouts, this natural and organic process is helpful in reducing the amount of lectins[26].

Other

In addition to domestic processes, there are also several industrial methods that are also useful in reducing and/or removing lectins from food.
These include autoclaving at around 121 degrees; dielectric treatments such as high-power – high pressure microwaves; or radio frequency (RF), at lower temperatures for delicate foods; or extrusion, mainly used to produce textured vegetable proteins from soya or peas; or even to produce breakfast cereals.
All methods are efficient in reducing lectin concentrations[35].

Conclusions

I am aware that what we know today about human biology may, tomorrow, be totally useless. Science is making giant and exponential strides, offering us new insights and horizons to discover every day; sometimes radically overturning the beliefs on which we have based our lives for years, decades.

This is why we have to stay up-to-date and rely on correct information, without giving in to fads or, worse, gurus on duty.
On the lectins, I hope I have shed some light; and without prejudice to any future discoveries by science, to date it confirms the wholesomeness of the foods concerned.
But then again, after all, a little common sense, observing what has been done over the centuries through domestic transformation processes, would be enough to make us feel reassured.
Personally, I have no doubts and will continue to base my sustainable and balanced diet on the foods that have always been considered healthiest; and I sincerely hope that after reading this objective analysis, you will do so too.

Happy revolution to all

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