These 50 Foods Are High In Lectins: Avoidance or Not? from Superfoodly

These 50 Foods Are High In Lectins: Avoidance or Not?

SuperfoodlyJanuary 25, 2017

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There are thousands of foods which have allergic reactions associated with them and in theory, it’s possible for any food to be an allergy candidate.
However the actual part of a food we can potentially be allergic to are the proteins and their pollens. Not all foods have those, or at least not in high concentrations.
Can you be allergic to apples? Yes but since they contain so little protein content, even if you are allergic, it’s unlikely you will have noticeable side effects like a skin rash, hives, or sneezing. Among those eaten, Gala apples have the least amount of protein and Starking have the most (1). The latter also tends to trigger more pronounced results in skin prick tests.

It’s not just a coincidence that the 8 most common food allergens are protein-rich (2):

• Milk
• Eggs
• Fish
• Crustacean shellfish
• Tree nuts
• Peanuts
• Wheat
• Soybeans

Many within these categories are also high lectin foods. Is that just a coincidence or do their presence play a part in symptoms?
It’s possible that your side effects might not even be from a soy, nut or dairy allergy. They might be caused be you having an increased sensitivity to a specific form of lectin poisoning.

Most common thing you’ve never heard of

You could spend a whole year reading nutritional websites and books, yet never come across this word. That’s a shame, because this is not an obscure topic. Lectin intolerance and toxicity affects all of us to at least some degree.
Lectins were discovered almost 130 years ago, in 1888. That’s well over a decade before aviation, something we have since mastered. Yet these commonly occurring compounds largely remain a mystery. And while you may not be flying everyday, it’s guaranteed that you are eating foods containing lectin on a daily basis.
Seems like something we really ought to know more about, right?
Glyca-binding proteins (GBPs) are a category of proteins which bind specifically to certain sugar molecules. The “glyca” is the same prefix you see in the word glycation. That describes what happens after a protein or fat binds with a sugar molecule (3).
This binding process can cause inflammation and the creation of advanced glycation end products (AGEs), which are compounds associated with numerous age-related diseases. It’s why the apparent anti-glycation benefits of carnosine are so intriguing.
While some is influenced by diet, most of the glycation in your body will take place no matter what you eat.

Source: Department of Chemistry, UC Berkeley (32)

There are two major categories of GBPs:

• lectins
• glycosaminoglycan-binding proteins

That last one is more relevant to pharmaceuticals (like heparin, a blood thinning medication) and how some infectious diseases work (like Streptococcus) (4). Since we’re focusing on food here, this second category will have to be a conversation for another time.

What are lectins?

Lectins are a defense mechanism which all life forms appear to have. Essentially, they are a low level toxin. The purpose of lectins is to discourage other animals from eating that life form. By triggering a negative reaction in the predator, that life form is then viewed as an undesirable food source. Hence, aiding its future survival.

Other names for lectins include agglutinins and hemagglutinins. When it comes to animal lectins, they’re almost always referred to as either agglutinins, glycans, glycan-binding proteins, or glycoproteins.
That’s why if you do a search, almost all of what you will see is related to plant foods.
As part of an avoidance diet, many folks are peddling a lectin free food list (or so they believe) by axing many grains, vegetables and fruits. They have suggested intolerance of them is causing weight gain, inflammation, leaky gut, and even major diseases.
That might be happening with some. But only picking on plants is premature.
Does meat like beef, chicken, and turkey have lectins? Yep…

Credit: Division of Molecular Biosciences, Imperial College London (5)

Not only do meats (vertebrate animals) have the same broad types/categories as plants, but they also have others in addition as seen above.
Whether you’re talking about meat, dairy, or eggs, those coming from animals are some of the least studied and most recent to be discovered.
What we do know though is that many of them bind not just to carbs, but also proteins and fats (6). That means overall, the animal forms may actually have a greater biological effect in the human body than those which are plant-derived.
Based on research to date, the highest overall animal source appears to be dairy.
Mammals only produce milk during reproduction to feed their newborns. Since reproduction is an animal’s most important task in life, it’s interesting to note that it also involves their most significant use of lectins – the mother’s milk is loaded with it.
This fends of predators – other species – from considering that milk as being their own potential food source. That ensures the newborn is more likely to get this vital source of food, rather than someone else. Keep in mind that predators include microscopic organisms, like bad bacteria and fungal infections in a baby’s digestive tract.
So why are these milk lectins nutritious for the baby, while being potentially poisonous to another species?
That’s how lectins work. They ensure the food is good for who should get it, but not good for everyone.
Is lectin the same as lecithin? No, they sound similar but are completely different things. While the former is a sugar-binding protein, the latter – lecithin – is a generic term for a broad category of yellowish-brown lipids (fats) which are found in both plants and animals.

What types of food contain the most lectins?

This is what a peanut lectin looks like. They are a rather large structure, involving dozens of different amino acids pieced together.

That’s not a straightforward answer, since each plant and animal has a unique type (or several). However if you were treating them all as equal and simply basing your answer off of percentage concentrations, these groups represent some of the highest natural sources identified so far.

1. Grains – Whole grains have more, since they are found in higher concentrations in the outer bran.
2. Nightshade fruits and vegetables – Such as white potatoes, tomatoes, eggplants, and peppers. Goji berries are also part of the Solanaceae family, which means they’re a nightshade.
3. Legumes – Beans, lentils, and peas.
4. Dairy – Pasteurized milk and dairy products may actually be worse because the heat destroys the naturally present SIgA, which is an immunoglobulin that may help neutralize lectins to some degree by binding to them (7).
5. Nuts and seeds – Excluding grain seeds, there is not much evidence to suggest that humans are sensitive to the types of lectins in tree nuts and most flowering seeds.
6. Yeast – It’s worth noting that “only a few reports are available” about the activity of yeast lectins (8).

Just because you don’t see a food on the list, that doesn’t mean it’s safe.
Scientists have only recently concluded that they are found in every plant and animal.
In fact, scientists have yet to identify a single organism, whether that’s something as large as an animal or as small as an insect or bacteria, which does not produce glycan-binding proteins. Whenever they have looked for them in a given species, they found them.
For example, research published in 2015 found them in dozens of different fish which were tested, including those we commonly eat like salmon, catfish, trout, tilapia, mackerel, and even eels (9).

Grains, nightshades, and dairy have long been scrutinized as being the worst. However that might be a premature conclusion. Scientists initially focused on those because their percentage content was obviously high. But less doesn’t necessarily mean better, since the types of lectin differ by food. Most have little to no research behind them.

The current mindset might be comparable to assuming a big truck full of dynamite is more dangerous than a small suitcase-sized nuclear bomb.
Quantity aside, the unique effects of each type need to be evaluated.
To give you an idea of their diversity, here is a table of lectins which have been discovered. These 50 are just a sampling of the thousands – perhaps tens of thousands – in our diet, most of which are unknown/unstudied. With the exception of dairy and wheat, many foods have only had one type researched even though they may contain several.

50 Lectin Foods (list in alphabetical order)
	Food	Lectin Name*	Abbreviation**
1.	Avocado	Persea americana agglutinin	PAA
2.	Bananas	Plantain agglutinin	none assigned (BanLec is shortened name)
3.	Barley	Hordeum vulgare agglutinin	HOV
4.	California crab	Cancer antennarius agglutinin	CCA
5.	Carrot	Daucus carota agglutinin	DAC
6.	Chickpea	Cicer arietinum agglutinin	CPA
7.	Cocoknut crab	Birgus latro agglutinin	BIL
8.	Corn	Zea mays agglutinin	ZMA (corn lectin is more often used)
9.	Eggplant	Solanum melongena agglutinin	SOM
10.	Elderberry	Sambuccus nigra agglutinin	SNA
11.	Fava bean	Vicia faba agglutinin	VFA
12.	Garlic	Allium sativum agglutinin	ASA
13.	Gourd	Luffia actangula agglutinin	LUA
14.	Jackfruit	Artocarpus integrifolia agglutinin (Jacalin)	JAC
15.	Kidney bean	Phaseolus vulgaris agglutinin	PHA
16.	Leek	Allium porrum agglutinin	APA
17.	Lentil	Lens culinaris agglutinin	LCA
18.	Lobster	sialic acid-specific lobster lectin	LAg1
19.	Mango	Mangifera indica agglutinin	MIH
20.	Milk (mammals, incl. cow)	A1 beta-casein (beta-casomorphin-7)	BCM-7 (name of 7 amino acid segment unique to A1)
21.	Milk (mammals, incl. cow)	A2 beta-casein	none assigned
22.	Milk (mammals, incl.cow)	phosphorylated whey glycoprotein	PP3
23.	Milk (mammals, incl. cow)	chitinase-3-like protein 1 (chitinase-like lectin)	Chi3L1 & YKL-40
24.	Milk (mammals, incl. cow)	pregnancy-associated glycoproteins	PAGs (numerous subtypes)
25.	Mung bean	Vigna radiata agglutinin	VRA
26.	Mushroom	Agaricus bisporus agglutinin	ABA
27.	Mushroom	Psathyrella velutina agglutinin	PSV
28.	Oat	Avena sativa agglutinin	AS
29.	Onion	Allium cepa agglutinin	ACA
30.	Pea	Pisum sativum agglutinin	PSA
31.	Peanut	Peanut agglutinin	PNA
32.	Peppers (incl. sweet bell and hot chili peppers)	Capsicum annuum GLP1	CaGLP1
33.	Potato	Solanum tuberosum agglutinin	STA
34.	Pumpkin	Cucurbita maxima agglutinin	CUM
35.	Rice	Oryza sativa agglutinin	OTL
36.	Rye	Secale cereale agglutinin	SCL
37.	Salmon	Salmon serum lectin	SSL
38.	Sesame	Sesamum indicum	SEI
39.	Shallot	Allium ascalonicum agglutinin	AAA
40.	Snail	Helix hortensis agglutinin	HEL
41.	Soybean	Soybean agglutinin	SBA
42.	Squash	Cucurbita pepo agglutinin	CUP
43.	Sweet pea	Lathyrus odoratus agglutinin	LOA
44.	Sweet potato	Ipomoea batatas lectin	IBL
45.	Tomato	Lycopersicon esculentum agglutinin	LEA
46.	Winged bean	Psophocarpus tetragonolobus agglutinin	PTA
47.	Wheat	Triticum vulgare agglutinin	TVA
48.	Wheat germ	Wheat germ agglutinin	WGA
49.	Wheat germ	Succinyl wheat germ agglutinin	sWGA
50.	Wine and grapes	Vitis vinifera lectins	none assigned
	*Name listed refers to the verbiage which is most commonly seen in medical and scientific papers. A given food can and will have multiple names – e.g. avena sativa agglutinin is the same as oatmeal lectin. **Abbreviation refers to that which is most commonly seen, some have multiple abbreviations – e.g. SBA and SBL for soy.

Remember the above is ranked table is by alphabetical order. Not many of them have had their exact percentages determined, which makes a list ranked by lowest concentration or potency impossible as of today.
If something does have a higher amount, that does not necessarily means it’s the worse type of food.
For example with tree nuts, the dietary issues tend to revolve around their high phytic acid content and allergy-producing proteins. Most research suggests their lectin content is not pro-inflammatory or causing other effects in humans. If you want to blame nuts for weight gain, it looks like that will fall squarely on their their high fat and calorie characteristics.

You will hear many health bloggers advocating for an anti-lectin or lectin free diet. That’s hilarious because it would be advocating for your death.

Why? Because these sugar-binding proteins are found in everything you eat, to at least some degree.
Some of those listed above, particularly the grains and milk, are singled out for having greater concentrations, but don’t interpret that as meaning meat, seafood, fish, and non-nightshade fruits and vegetables don’t contain lectins, because all those do too!
In short, that makes lectin free eating impossible. Especially since some types are not destroyed by heat or gastric acids (more on that below).
Since we’re talking about an unknown number of different types, you can’t put them all under the same umbrella.
If two foods had a 1% concentration – but they were different types – then would you be able to say they are equal?
Not necessarily.
Some types appear to have no effect in humans, while others may be inflammatory or even deadly.

castor beans

Ricin is one of the most deadly poisons known to mankind. It is a lectin found in castor beans. Just an isolated speck of it might be all it takes to kill you.
On the other hand, you could eat 10,000 times that amount in a meal of black beans… but it’s a different type you’re eating.
Now you may wish you were dead from all the gas and bloating after that Chipotle burrito, but it’s not going to stop your heart from beating.

Not always bad?

What about their beneficial effects? Any buzz you may hear is that lectins are really bad for you. That their intolerance makes you fat or has inflammatory side effects.
What they often fail to mention is that depending on the type, they can have a neutral effect – not being bad or good – or even offer benefits for human health (10).
That’s right, lectins can be healthy and good for you! You can’t paint them all with the same brush.
It’s kind of like people who start with the premise that bacteria are bad. True, many are dangerous to humans, but many are beneficial and actually necessary for our survival. Without your gut flora, you would not be able to digest nutrients and would die.
You can’t avoid lectins entirely. Common sense tells us that if their consumption was entirely bad for us, then no one – humans or animals – would have them in literally everything they eat.

Why they affect us differently

The rationale for how lectins work the way they do is actually quite brilliant.
As a human, if you were designing them for your own body, your goal would probably be to make them harmless for your species, but toxic to all other life forms who may want to feed off or eat you.

That would be the best approach to ensure your survival, right? Because whether it’s a bear, a lion, a dog, or even a mosquito… none would want to eat you, because they would associate you (humans) as being toxic.
Well, if you designed your lectins that way and each species did the same for theirs, what would be left to eat on this planet?
We would all be toxic to one another!
On the flip side, being edible to everyone is having the pendulum swing too far in the other direction. If the berries on a bush could be eaten by every animal and insect, then how would it ever survive? It might not, because it would have a bullseye on it from every species who encountered it.
But let’s say you took that same bush and made the berries toxic to mammals, but safe for birds.
Now you have a balance. The life of the bush is protected from most, but its life is extended to some as a food source.
No one can know why God works the way God does, but this theory is the best we can come up with using our very limited human minds.

Different effects within same species?

We’re not all clones of each other.
Within the past several decades, science has gained much greater understanding of the biological differences within the same species. Differences not believed to exist previously, or thought of as rare genetic mutations, or perhaps fringe theories concocted by rogue minds.
For example, sexuality. Thanks to newer MRI technology, scientists have begun realizing there really is a difference in the brains of straight and gay people. The latter exhibiting patterns more comparable to the opposite gender than their own.
Naysayers will claim that different brain pattern is due to what they view as years of deranged and deviant sexual behavior.
Then how do they explain the fact that these brain pattern changes are seen in “gay acting” children (who later in life are gay) even before they go through puberty, and before they have any type of sexual experiences or even fantasies of such? That negates the deviant behavior theory, since the brain changes can be seen beforehand.
Further along than the topic of sexuality is what science now realizes about allergies. What we know and accept today is even different than a couple decades ago. We now understand how prevalent of a problem food allergens are.
Yes, a lot of people are totally delusional and simply follow gluten free diets as a fad without any scientific understanding or medical testing done to diagnose a disease/sensitivity.
But even setting those types of people aside, thanks to more research and testing in recent years, the medical community understands that food allergies are really a bigger problem than previously thought. They’re not just rare disorders. They can have serious consequences in our life and may worsen – if not be directly responsible for – a number of autoimmune diseases and perhaps others.
How this all relates to lectins is that even more recent than these controversial topics is the concept that yes, lectins really do seem to affect some people differently than others, possibly be a large degree.
Research is starting to find that some people may be affected by nightshades like potatoes, while others can eat them their entire life without any adverse side effects whatsoever.
Or maybe it’s a vegan who can eat beans in abundance with minimal farts or other symptoms, while some people eat just a smidgen and experience a total digestive disaster.

Why are lectins bad?

As mentioned above, you can think of them as a low level toxin. Just like chemical poisons, how they may (or may not) harm you depends on the type and amount encountered, along with your body’s unique biology.
When harmful, lectins and inflammation go together like two peas in a pod, pun intended.
But the cause of this inflammation can differ depending on whether it’s occurring inside of your GI tract or outside of it (in your bloodstream).
Gastrointestinal symptoms like flatulence, bloating, stomach aches, diarrhea, and that whole gamut of side effects can occur with beans. Many blame lectins for that, but it’s the oligosaccharides (sugars) such as raffinose and stachyose which are causing that. The fact that beans are high lectin foods is irrelevant to those side effects, at least for most people.
Remember that part we said about foods being edible for some species but having side effects in others?
When it comes to beans, peas, lentils and other legumes, humans don’t make the enzyme known as alpha-galactosidase which is needed to digest them.
So they ferment in our digestive tract and that is what’s causing the side effects.
However many other species, including other mammals, do have the enzymes and can eat them just fine. For us humans, popping a couple Beano tablets can work wonders at combating gas and bloating, since it introduces enzymes with your meal which break down these tough to digest beans.

Due to these missing enzymes, it’s why raw food dieters should avoid most legumes if they’re going to refuse cooking them.

The heat of cooking, at least with legumes, greatly breaks the oligosaccharides. It also destroys lectins. This is why the lectin avoidance diet should really be re-classified as the proper food preparation diet in many scenarios. Because people are confusing lectin content in beans and the associated side effects, when they are largely unrelated. With tomatoes, cooking destroys the content.
In short, the right food prep methods may be just as effective as avoidance.
That’s not to say the irritation and inflammation from lectins in beans can’t be a major problem though. Certain types and concentrations definitely can be.
Red kidney beans contain the toxic phytohaemagglutinin in a very high concentration. Eating them raw or undercooked will lead to severe side effects 1 to 3 hours later, including vomiting and nausea. That poisoning will happen in anyone. Abdominal pain and diarrhea can result, too.
To put it in perspective, here’s how red kidney beans test out for their lectin content (11):

• Raw = 20,000 to 70,000 hau (hemagglutinating unit)
• Fully cooked = 200 to 400 hau

That’s a 99% or greater reduction from the heat of cooking. By that simple act, you have turned them into a low lectin food.
This type of bean is by far the worst dietary offender, as even white kidney beans have about 67% less than their red cousins. Broad beans are 90 to 95% less. The content in soy is bad but it’s easy to neutralize (more on that below).
The side effects of phytohaemagglutinin in kidney beans are taking place in the GI tract. Or triggering symptoms which are directly caused by nerve stimulation down there (i.e. feeling nauseous).
For Crohn’s disease, IBS, ulcerative colitis, and other GI disorders, it’s easy to understand why any added inflammation in the tract – even if minimal – could be a worsening factor in them, right?
But you hear people blaming lectin intolerance and toxicity for everything from asthma to rheumatoid arthritis, and even conditions of the brain like autism and Alzheimer’s. Things like that are clearly unrelated to the digestive system, if these lectins are not being absorbed and therefore remaining isolated to the GI tract. Right?
Maybe not.
It is correct that most lectins are quite resistant to stomach acids and the digestive process. For that reason, they were not believed to be absorbed. Meaning, they could not enter your bloodstream and flow to other parts of the body (like the brain, kidneys, liver, or joints).
The history of lectins really changed in 1989, when it was first discovered that some of these indigestible proteins are instead permeating through the gut wall and then having free reign to run wild in your blood steam. They can then deposit themselves in distant organs (12) (13).
That may not seem surprising to read, but you need to understand that when something is not absorbed during digestion, it’s typically assumed that it does not enter the bloodstream and therefore is harmless outside of the GI tract.
For example the heavy metal barium, which you drink for CT scans of the abdomen, is highly toxic.
However in the form of barium sulfate, which is the form used for these radiological purposes, it is not believed to be absorbed at all and therefore is considered safe, because presumably all of it passes through the digestive tract fully intact without entering your bloodstream.
That was how scientists previously thought of the indigestible glycoproteins.

When this discovery came about in 1989 that some indigestible lectins may actually be absorbed and entering the blood stream, it changed the whole paradigm of how we must evaluate them.

Suddenly, the fact that our digestive juices and gut flora don’t break them down does not automatically guarantee their safety. Because they still might be entering our bloodstream through what’s been coined leaky gut.

Image credit: BallenaBlanca (Own work) [CC BY-SA 4.0], via Wikimedia Commons

Technically known as a hyperpermeable intestine, leaky gut is a term used to describe areas of the intestine which are more porous. In other words, they have “holes” in their protective lining and therefore, substances which normally would not be allowed to enter can do so. Having your average dietary sugars “leak” through your intestinal wall is probably harmless. The concern isn’t about the normal things which your body would be absorbing regardless.
The real worry is about stuff getting through which your body doesn’t want. Toxins, heavy metals, and large foreign molecules which your body has no nutritional use for.
How lectins and leaky gut may be related is by making the condition worse. Some theorize these glycans may even be triggering it in the first place, in an otherwise healthy GI tract which does not have abnormal “holes” in it.
How lectins function to do this is by irritating the intestinal lining.
The tight junctures in the lining are normally closed to prevent undesired substances from getting through. After being irritated by some types, it has been found that these junctures of mucosa cells are stimulated to open up – like a door – allowing unrestricted access for things to flow through and go directly into your blood stream.
It’s this leaky gut syndrome which is why there is evidence piling up to suggest lectin irritation might be affecting seemingly unrelated diseases, too.

Diseases caused by lectins

It’s important to reiterate how little is really known about these compounds. There are thousands of different types of lectins in our diet. Among those identified, only a small fraction have been extensively studied.
Furthermore, there are thousands of different complex carbohydrates (sugars) which are used by our cells for signaling.

So not only do we not know how many lectin types there are, but to further complicate matters, we have no clue how even the most common ones interact with all the different types of sugars which they may encounter in the body. Some interactions may be harmless, others not.

Due to the many unknowns, no one can say for sure which diseases might be caused by their presence. Given the many different types of these sugar-binding molecules, it’s a bit too generic to simply say they are a cause in general.
Even if they do, it doesn’t mean all lectins are the problem. Most likely, it’s a few very specific types and even with those, they’re probably only affecting some – not all – sufferers of a given disease.
While unproven, there have been accusations that lectins may have a role – either as a direct cause or a worsening factor – in some cases of the following diseases and health conditions:

• ADD/ADHD
• Adrenal insufficiency
• Allergies
• Asthma
• Atherosclerosis
• Autism
• Cancer
• Candida fungal infections
• Celiac
• Crohn’s disaese
• Congestive heart failure
• Diabetes type 1
• Diabetes type 2
• Fibromyalgia
• High blood pressure
• High cholesterol

• Hypoglycemia
• Irritable bowel syndrome (IBS)
• Low DHEA
• Low testosterone
• Lupus
• Multiple sclerosis (MS)
• Obesity
• Rheumatoid arthritis
• Schizophrenia
• Thyroiditis
• Osteoarthritis
• Parkinson’s disease
• Polycystic ovary syndrome (PCOS)
• Post traumatic stress disorder (PTSD)
• Premenstrual syndrome (PMS)
• Ulcerative colitis

Again, it’s important to reiterate not a single one of those diseases has been proven to be caused by glyca-binding proteins. And those proposing such theories are not inferring they are causing every case. With most things on the list, the beliefs are that their role is only as a worsening factor, not a root cause.

Wheat lectin vs. Celiac disease

In many ways, the gluten free diet seems like a total scam.
Yes, it is true that diagnosing Celiac or heightened gluten sensitivity is complicated. There’s not really a simple test to do so.
Often times, the diagnosis is based on at least two different food allergy tests. The most extreme being a biopsy of the small intestine to see how the lining has been affected. Since that’s a surgical procedure, more often it is blood testing used to check for gluten antibodies and/or a “poop test” where the same is done with your fecal matter.
There is also genetic testing to look for certain alleles which correlate with Celiac disease, but that is not a reliable diagnosis in and of itself.
However it’s diagnosed, only a very small portion of the population – in the low single digits percentage – tests out positive for these. Or to be more technically accurate, tests positive for having either Celiac or substantially higher elevated gluten antibodies (everybody will have at least some antibodies, for all foods).
The exact percentage is highly disputed, but it is a low number. For the sake of math, let’s say 7% of the population has a gluten allergy/sensitivity, which is a figure that’s sometimes cited (14).

If it is only 7% of the population, then why do three times that number – 21% of Americans – try to “actively include” gluten free in their diet. Many of them claim it makes them feel better and helps with weight loss.

That 21% is the average of 19% for men and 23% for women, according to a Gallup poll (15).
Is it because of the placebo effect?
Is it because the other 14% are uniformed idiots?
The answer to both is yes, to at least some degree.
But within those 14%, there is evidence to suggest legitimate reasons why they might experience real improvement in their health, even though their gluten sensitivity is completely normal.
Brain fog from lectins is a common theme you will hear, but the truth of the matter is that even if they’re entering through a leaky gut, that doesn’t necessarily mean they can get into your brain. Your blood brain barrier (BBB) blocks many things, primarily large molecule.
To get through, large molecules need shuttle mediated transport (something to latch onto, which can permeate the barrier).
The mass for one type of chicken lectin was found to be 69,000 daltons (16). For tomatoes, one is 65,633 (17). Phytohemagglutinin-L (PHA-L) isolated from the red kidney bean has a weight of approximately 120,000 (18).
Leeks and taro are also foods with mannose binding lectin (MBL) and those are often high molecular weights.
In humans, 600,000 daltons is what one particular lectin specific to mannose and N-acetylglucosamine residue tested out at. A smaller sub-unit of it was still 31,000 (19).

How big can they be to enter the brain?

What the structure of wheat germ agglutinin looks like.

400 to 600 daltons is considered the max for being able to penetrate the BBB (20). While some scenarios allow for larger, you’re not talking tens of thousands of daltons.
Wheat germ agglutinin (WGA) is what discourages insects and bacteria from eating the wheat kernal. That’s a size of 38,000 daltons (21).
So how would wheat lectins, which are 38,000 daltons, get through the blood brain barrier, which only allows up to around 600?
That’s not exactly like squeezing into a tight pair of jeans. You need a magic trick here, because if you’re a WGA lectin, it’s like having a butt which is 60x fatter than the opening of the doorway.
Well, there might be a magic trick which can make that happen.

In 1988 it was discovered that wheat lectins could pass through the blood brain barrier of mice and rats through what’s called adsorptive endocytosis.

That was discovered by the University of Maryland (22). In the 30 years since, there’s been almost no research involving wheat germ agglutinin and adsorptive endocytosis. So whether this happens in humans appears to be unknown and obviously, it’s not easy to measure without opening a human brain or using things like radioactive tracers, which no one in their right mind would voluntarily do.
While there is some evidence that dairy can do the same, when it comes to foods, Dr. William Davis claims that wheat is unique in its ability to cross the BBB.
Different than wheat lectin and inflammation in the body, Dr. Davis talks about how when gluten is digested in the stomach by pepsin, it is broken down into various short chain sized polyproteins, which have been found to enter the brains of rats. They allegedly bond in the brain, because these wheat polypeptides are similar to endorphins.
Dr. David talks about this in his #1 New York Times bestseller, Wheat Belly: Lose the Wheat, Lose the Weight, and Find Your Path Back to Health.
If that theory is true, maybe that’s why such a large number of people report less brain fog and other Celiac-like symptoms when they go gluten free.
Ultimately though, research on how wheat lectins and leaky gut might affect the brain is only just beginning.
Before you go on a wheat free diet, it is worth noting that research has found that WGA may actually enhance the natural anti-cancer (tumoricidal) activity of human monocytes (a type of white blood cell). This was seen with select types of cell lines for bladder cancer, melanoma, kidney cancer, and glioblastoma (brain cancer) which were tested in the lab (23).
Like anything, there are pros and cons to consider.

Lectin avoidance diet?

This is one of those topics where both sides need to be humble and admit they don’t know what they don’t know.
The naysayers will call this avoidance diet a hoax, making the argument that foods containing lectins have been part of human history from the get-go.
That is true, but in what quantity?
In the hunter-gatherer days, perhaps a few kernels of wheat, barley, or other grain would be picked by hand. But given the labor involved, you can bet they weren’t depending on it as a staple of their diet.

When milling and the production of flour came about, it was desired to discard the bran (outer shell) of the grain and make the flour using what’s inside. Therefore, much of the grain lectin was discarded.

That’s why the amount of lectin in white rice is lower than brown rice.
Where did peasant bread get its name? Here’s a clue, it wasn’t made using white flour – that is the most labor intensive and expensive form to produce.
Until just a few decades ago, white bread was considered superior. Basically, the tables have turned – what was considered inferior for thousands of years, whole grains, are now considered preferable and healthier than refined white.
Could this shift have anything to do with the seemingly increasing rates of food allergies OR symptoms masquerading as such, which might be caused by lectins in grains?
You can’t say for sure one way or another.
For that reason, if you are experiencing health issues, it certainly would hurt to try a lectin diet. That’s where you selectively remove a type – like nightshades – and see how you do over the period of a few weeks without it.
Then rinse and repeat with other types. You might find you are intolerant to certain type(s).
But as we said above, lectin free foods are a misnomer. You can’t remove them entirely, but learning how to reduce lectins in food is a viable diet plan.

If they’re in everything, where do you begin?

Great question.
Just because a given food might have more of them, that does not automatically mean it’s a problem.
This is because there are thousands of different types in your diet and their effects in the human body can vary greatly. From lethal poisoning like ricin, to having no effect at all.
With that caveat said, based on the limited knowledge known today, even though they’re not be apples to apples, it does seem logical to start by reducing foods that contain lectins in high amounts.
Sure, if there was a 1% concentration in a milk product and a 1% concentration in a wheat product, that doesn’t mean they’re equal in effect. Nor does it mean they’re better than a food with a 2% concentration of a different type.
In an ideal scenario, you would be able to weigh each type accordingly. But with the exception of a few specific foods like kidney beans, any health effect they may have is poorly understood. For that reason, starting with the elimination of the highest known sources isn’t a bad idea.

How to reduce or remove lectins?

Rather than avoid these foods entirely, the preparation method is arguably far more important.
Though for some types of foods, cutting them out entirely may be the only effective method for real reduction.

Grains

When the endocrinologist Joseph Charles Aub first discovered wheat germ agglutinin in 1963, its resistance to heat was among the first characteristics noted (24). Yet it was still destroyed after 15 minutes at just 70° C (158° F).
Later research did reportedly detect heat-stable lectin activity in gluten from gliadin and the acid-soluble glutenin fractions of gluten. This was different from the activity coming from wheat germ, as cross contamination was ruled out (25).
Whether it’s gluten grains like wheat, barley, and rye, or GF alternatives like oats, sorghum, and millet, you may want to try switching to baked goods and cereals made with more refined flours, not whole grains or bran, since those contain high amounts of lectin. There will be an adverse glycemic effect in doing so and for that reason, consult your doctor beforehand if you are a type 1 or type 2 diabetic.
White rice is also high glycemic, but it contains fewer glycoproteins when compared to brown rice.
Does quinoa have lectins? Of course, but they have not yet been studied. There isn’t even a designated abbreviation for quinoa agglutinin. Being a gluten free seed rather than a grain, it’s possible that quinoa might have an effect similar to other flowering seeds like sunflower, flax, and hemp. Those have no obvious impact in humans. But that is only a theory.
Like quinoa, buckwheat is another gluten free pseudo-grain. It’s related to rhubarb. It might be another low lectin food, or more accurately said, one which is less likely to have dietary side effects when compared to gluten, gliadin, and wheat germ agglutinin. But with no published research on buckwheat lectin, any advantage it may offer non-Celiacs for digestive tolerance is speculative.

Legumes

mung beans

How to remove lectins from beans will involve soaking them overnight, rinsing and draining, then thoroughly cooking. They are not something you want to undercook!
If you don’t have the time to soak canned beans overnight in the fridge, that’s fine, but just make sure you rinse them well before cooking.
The heat will almost entirely destroy lectins in beans, as pointed out in numbers above for kidney. You can entirely deactivate lupin, fava, and soybean lectins when you boil them at 100° C (212° F) for at least 10 minutes (26).
With lower temperatures, that’s not the case. Cooking legumes at 70° C (158° F) for several hours “has little or no effect” (27).
Soy milk is heated (pasteurized) but is that for at least 10 minutes? The manufacturers don’t say. For that reason, veer on the side of caution and avoid soy milk if you are worried there might be active agglutinins in it.
Peanuts are actually a legume. Since this “nut” is always sold roasted, a lower amount of peanut agglutinin (PNA) would be expected.
If you’re using prepared fresh or dry beans/lentils, try sprouting them before cooking. The germination process further reduces the amount they contain.
Raw coffee beans will contain large amounts. Considering how thoroughly those beans are heated – probably more than any other food or drink in your diet – your cup of joe is likely quite safe. Coffee has not been researched though pre and post roasting.

Dairy

Neutralizing lectins might be helped by unpasteurized milk, since more SIgA is said to be present (which can be destroyed by heat). However we live in a country where buying or selling unpasteurized milk is a criminal offense in many scenarios. Even if you got your hands on it, there will still be a high amount of lectins in milk regardless.
The suggestion that grass fed milk, butter, or ghee contains less is not something which is backed by studies.
This is why forgoing dairy altogether for a while and seeing how you do is a good strategy. Aside from milk, that also means no butter, cheese, ice cream, and other derivatives during your test.
Vegan milks are made with nuts and oils which generally have low lectin, or the forms they contain have little to no apparent effect in humans. Almond milk, cashew, and other nuts appear to be safe.
Intolerance from coconut oil and others used to make them won’t be a problem either, since refined oils are pure fats (not proteins).
Be aware though how many almonds are in the milk, because it’s not many!

Potatoes

The most commonly consumed nightshade, potatoes are about 6.5% lectin content on average, which comes primarily from solanum tuberosum agglutinin (STA) (28).
Whether it’s yams, sweet potatoes, purple potatoes, potato starch, or any other form… they’re all going to contain high amounts of glyca-binding proteins. However, the sweet varieties are not part of the nightshade family.
The potato lectins are very stable under heat, acid, and base solutions. This is believed to be due to its high carbohydrate content and the disulfide bonds formed with them.
The STA can be deactivated under oxidative conditions and is “easily inactivated” by sodium hydrogen sulfite, which is also known as sodium bisulfite (29).
That chemical was a food additive, but for use on fruits and vegetables, the the FDA banned it in 1986. This was after it had killed 13 people by triggering asthma attacks and injuring countless others. (30). That rules out its use as a method for reducing lectins in potatoes. It is still used for making wine and beer though.
As far as oxidative conditions which might deactivate them, many cooking methods fall under that category. However the baking and frying of potatoes will produce high amounts of acrylamide, a class 2A carcinogen according to the World Health Organization.

Tomatoes

Very little is published on pepper and eggplant lectins, but tomatoes have more research.
There is a rumor going around that lectins in tomatoes are enhanced with the heat of cooking. That’s incorrect. It’s actually the antioxidant lycopene which has enhanced bioavailability from heating (31).
Since they’re often eaten raw in salads, tomato lycopersicon esculentum lectin (LEL) often bypasses any heat and for that reason, it has been estimated that the average American consumes 200 mg per year of it.
Now you have two good reasons to pig out on that plate of spaghetti marinara. Maybe even three, if you’re using GF pasta made with refined flour. But do please cook those noodles extra al dente, as that can help lower its glycemic impact