Lectins Their Damaging Role in Intestinal Health,
Rheumatoid Arthritis and Weight Loss
Carolyn Pierini, CLS (ASCP), CNC
Located on the surface of cells of all living things lay many thousands
of different complex sugar molecules (glycoconjugates) projecting
outward from their loose anchors like moving antennae. Genetically
unique, these molecules comprise a protective coating for the cell and
perform many functions including cell recognition and signaling. Lectins
are a class of protein molecules capable of using these sugar moieties
to bind to the surface of cells. Lectins provide the way for one
molecule to stick to another molecule without any immunity involved.
Lectins play a wide role in health, but their ability to influence the
inflammatory process indicates they are involved in inflammatory bowel
disease, rheumatoid arthritis and even weight gain. Lectins' potential
involvement in many aspects of our health caused DJ Freed, MD to state,
"Lectins are causes in search of diseases."
This article will introduce you to the world of lectins, the "sticky
proteins" we deal with from day to day in our diets and our bodily
systems. Furthermore, you will learn how you can build up your defenses
against what could be a hidden cause behind many of our health concerns.
Learning About Lectins
Lectins, not to be confused with the endocrine hormone leptin, are types
of proteins commonly found in nature in foods such as fruits,
vegetables, and seafood, but especially grains, beans and seeds. They
are present in about 30 percent of the American diet and are not
degraded by stomach acid or proteolytic enzymes, making them virtually
resistant to digestion. Microbes carry lectins and use them for
attachment to the host cells. The human body contains lectins: 1) On the
vascular endothelial linings (selectins) in order for blood cells to
escape into the tissues; 2) In the liver to capture microorganisms, and
3) As opsonins, substances that coat foreign antigens, making them more
susceptible to phagocytosis (the process where immune cells digest and
destroy foreign invaders) by the white blood cells. C-reactive protein
(CRP) and mannose-binding protein (MBP) are two examples of opsonins.
The word "lectin" comes from the Latin phrase, "I choose," a befitting
word choice since lectins are very specific as to what they will bind
to. Lectins are also called agglutinins because in their binding to many
cell surfaces they cause agglutination (cell clumping) reactions. Ricin,
for example, from castor beans is such a potent lectin that just a
minute amount is capable of causing death due to massive clotting of red
blood cells from agglutination. Ricin even has been used as a murder
weapon in espionage.
A lectin serves the plant as a type of primitive protection system
analogous to an antibody but in a non-immune model. Likewise, human
lectins in our bodies also act protectively but as part of an immune
system. Known for a century, lectins form a diverse group of molecules
of varying molecular weights and shapes and contain multiple binding
sites. The only thing lectins have in common with each other is their
ability to bind to sugars. Lectins bind to the terminal sugar, the "glyco,"
portion of glycoconjugates found on cell membranes. If the sugars are
bound to proteins they are called glycoproteins or bound to fats they
are called glycolipids. Collectively they are called glycoconjugates of
which 11 percent of the human body is composed.
The important point is that some of the lectins consumed in everyday
foods act as chemical messengers that can in fact bind to the sugars of
cells in the gut and the blood cells, initiating an inflammatory
response. In wheat, gliadin, a component of gluten and an iso-lectin of
wheat germ agglutinin (WGA), is capable of activating NF kappa beta
proteins which, when up-regulated, are involved in almost every acute
and chronic inflammatory disorder including neurodegenerative disease,
inflammatory bowel disease, infectious and autoimmune diseases.1 WGA
needs more recognition as an important dietary problem. Scientific
literature shows that dietary lectins can dramatically reduce natural
killer (NK) cell activity directly and through disruption of intestinal
flora. Natural killer cells are one of the body's most important
defenses against viruses and other invaders.
Most dietary lectins will also stimulate polyamine production in the
gut. Polyamines are important growth factors that may have negative
effects if levels become imbalanced. Excess polyamine production
initiated by lectins may be the result of an effort to repair the damage
to intestinal microvilli caused by lectins. In addition, a high
polyamine level may also decrease NK cell populations2, can contribute
to halitosis (bad breath), and is considered an important biological
marker for colonic precancer. 3-6 A number of animal studies have shown
that an increase in polyamines caused by a high lectin diet resulted in
increases in the size of the intestines, liver, and pancreas.7
Lectins, Food Allergies and Intestinal Concerns
There is an abundance of literature from the most prestigious journals
that lectins such as WGA initiate allergic reactions in the gut causing
the release of IL-4, IL-13, and histamine from human basophils producing
noticeable allergic symptoms.8-9 WGA has also shown to interfere with
protein digestion and increase gut permeability.10-11 Peanut lectin,
kidney bean and soybean lectins are other examples of lectins that have
influences on bodily tissues. On the bright side, the lectins in broad
beans (VFA), jackfruit (JAC), and culinary mushrooms (agraricus
bisphorus) have been shown to slow the progression of colon cancer.12-13
Lucretius said, "One man's food is another man's poison" and lectins
give us part of the reason why. It is our individual genetic
inheritances that determine how and to what degree lectins can affect
us. Almost everybody has antibodies to some dietary lectins in their
bloodstream. Many food allergies are actually immune system reactions to
The trend toward consumption of less processed grain foods, although
more nutritious in many respects, results in consumption of more lectins.
After ingestion, most dietary lectins bind to the absorptive microvilli
of the small intestine (the microvilli are the tiny finger-like
projections on the epithelial cells). From there lectins may gain access
into the blood and lymph system through a process called endocytosis
which carries the intact lectin across the microvilli membranes as a
vesicle.15 Then, the lectins may enter the liver, pancreas and systemic
circulation. It is estimated that about 5 percent of ingested lectins
enter the body systemically, where, depending on the lectin and
depending on the person's unique glycoconjugates, lectin binding occurs
on other tissues such as nervous and connective tissue and the bladder,
which are very sensitive to the agglutinating effects of lectins. It is
a clinical observation that the complete avoidance of wheat lectins will
help ameliorate the symptoms of interstitial cystitis. The reactions of
lectins in the gut are more potent since the gut is more heavily
glycosylated (more sugar receptors). As intestinal cells age they become
less glycosylated due to the loss of glycoconjugates. The intestinal
lining of people with Crohn's disease and IBS (irritable bowel syndrome)
appear to be more sensitive to the effects of food lectins because the
lining is constantly being replaced by new tissue that is made up of
immature cells that are more glycosylated and thus more susceptible to
lectin attachment. It becomes a vicious cycle. Blood group antigens as
glycoconjugates are found on the surface of cells lining the digestive
tract in addition to the blood cells and are frequently the target of
specific lectins resulting in agglutination reactions. The same
reactions in vitro are conducted daily in the clinical lab blood bank as
Lectins have many other applications in the clinical laboratory from
identification of microorganisms to cancer research where lectins serve
as probes to investigate the working of the cell through its surface
biology. Lectins have been used as carriers for the delivery of
chemotherapeutic agents. Mitosis (cell division) can be enhanced with
lectins such as pokeweed lectin (PWA).
Lectins and Rheumatoid Arthritis
The fact that lectins appear to aggravate existing inflammatory
conditions can be seen in the example of rheumatoid arthritis.16-18 The
RA antibody is different structurally from a normal antibody in that the
side-chain sugar, galactose, is replaced with N-acetyl glucosamine, the
sugar for which the wheat germ lectin (WGA) is highly specific. This may
point to why patients with rheumatoid arthritis feel better on a
wheat-free diet. The defective RA antibody has also been shown to be
reactive with the lectin found in the common lentil bean. According to
the eminent immunologist David Freed, "Of the various rheumatogenic
foods, wheat and other grains top the list. Avoidance of these is
frequently the only dietary maneuver required, especially in early
cases." He proposed that ingested wheat lectin (and other dietary
lectins) enter the bloodstream from the intestine and bind strongly to
connective tissues (which contain considerable quantities of
glycoprotein) and skin proteoglycans making them stiff.19 It is a
clinical observation that inflammation of the gut is associated with
inflammation of the joints. It has been also observed that the pain and
inflammation of fibromyalgia may stem from or be contributed to by
intolerance to wheat lectins. In fact, lectins are capable of
intensifying the effects of autoimmune disorders in general. Nightshade
vegetables like potatoes and tomatoes are very high in lectins and are
known to trigger the symptoms of arthritis.
Sticky Proteins in Weight Management
A very important and interesting feature of some lectins is their
ability to mimic hormones. As one can imagine, this could contribute a
significant impact on metabolism. The hormone insulin stores excess
carbohydrates (glucose) as fat. It accomplishes this by attaching itself
to the insulin receptor found on the fat cell. Under stimulation from
insulin, the fat cell becomes more permeable to glucose, which would
otherwise remain in circulation. With mission accomplished, the insulin
hormone then disconnects to its receptor. In many people, lectins found
in lentils, green peas, corn, potatoes but especially wheat germ
agglutinin (WGA), are known to bind to the insulin receptor giving the
fat cell the same message that insulin gives, namely to make fat. The
lectin, however, due to a lack of feedback inhibition, remains
indefinitely attached to the receptor giving the cell a constant message
to make fat.20-25 This perhaps explains why many weight loss programs
that include a moderate-to-high amount of carbohydrate (especially
modern grain) fail.
One other point with regard to lectin contribution to weight gain is the
fact that lectins have been shown to block digestive hormones. WGA can
bind to the receptor for cholecystokinin (CCK), a hormone involved in
appetite control, suppressing its function.26-27 This essentially leads
to an increase in appetite and impairment in the release of digestive
Detrimental Dietary Component
Consider the fact that there are many varieties of wheat grown
worldwide. Ancient wheat species had much lower protein contents than
the modern varieties. Lectins are proteins. Increasing the protein
component has also increased the lectin load with the resultant
potential for inflammation and metabolic disruption. Genetic altering of
grain plants (GMO) has also changed the lectin content.
Interestingly, lectins are destroyed in the sprouting process, which
allows for a safer form of grain consumption, not to mention that the
sprout is generally higher in overall nutritional value than the seed.
Organic, sprouted grain bread products (with no added gluten) appear to
be the safest and healthiest way to reap the nutritional benefit of
grain without the lectin burdens.
Some lectins are resistant to heating by cooking. As a side note,
soaking beans before cooking them reduces the lectin content
dramatically. Most people do not know why beans prepared this way makes
them easier to digest but it is simply because the water-soluble lectins
have been nearly completely removed through the changing of the water
Protecting Against Lectins
Because lectins are so prevalent in a typical diet, undertaking a
supplement regimen to help combat the damaging effects of lectins can
help contribute to optimal health, improve the health of the intestinal
tract and contribute to weight loss. Certain seaweeds, especially those
high in the sugar fucose (Bladderwrack) and mucilaginous vegetables like
okra have the ability to bind to lectins in a way that makes them
unavailable to the vulnerable cells of the gut. These foods act as
sacrificial decoys and attach to the problematic lectins that would
ordinarily attach and bind to gut epithelial cells. A specific
glycoprotein, N-acetylglucosamine (NAG), is also a favorite target for
dietary lectins and is concentrated in connective tissue.
Supplementation with NAG is an excellent strategy for lectin protection.
Another sugar with similar activity is D-mannose, which is capable of
binding to lectins located on the cells of microorganisms. Some bacteria
responsible for urinary tract infections contain lectins specific for
the sugar mannose and use these lectins to bind tightly to mannose-rich
tissue in the bladder walls, initiating urinary tract infections (UTIs).
28 As with Bladderwrack and NAG, supplementation with D-mannose provides
a decoy for these lectins and protects the bladder. Supplementing prior
to a meal with these decoy sugars allows for the binding of potentially
harmful lectins and protection from attack. This concept of lectin-shielding
devices has exciting clinical application now and in the future.29
The subject of lectins is very broad and deserves more discussion. There
are even some lectins that are beneficial to the body, such as those
found in some species of edible snails, which may be capable of
preventing the metastasis of cancer cells. 30 The involvement of lectins
in our health and their relationship to degenerative disease is still an
emerging science. Studies performed on animals will continue to be the
model in the future for the study of lectins. The glycosylation of the
human gut is basically similar to that of higher animals and it may be
confidently predicted that the effects of dietary lectins will have
similarities in both humans and animals. In short, dietary lectins, by
their chemical reactivity with cell surface receptors on the intestinal
epithelium, are metabolic signals for the gut and are capable of
modulating immune and hormone functions.14
source of nutrients and supplements.
did we qualify them ?
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