“Legumes = lectins = leaky gut = leaky brain.
I’ll get my carbs and protein elsewhere.”
I shared this quote from an individual I encountered in
another post, and I’ve included it again here because I think it’s the perfect
example of the true fear and confusion that exists surrounding whole grain,
legume, and lectin consumption. Not surprisingly, the individual quoted above closely
adheres to the Paleo diet, and it has been my observation that much of the
popular anti-grain and legume sentiments generate within this community, as well
as in the general low-carbing crowd. These two dietary sects renounce
grains and legumes (yet interestingly enough make Paleo Cupcakes and Primal Cookies on the weekend!),
but I won’t expound upon the virtuous or faulty aspects of these diets in this
post—as always, eat whatever diet suits your health best (though I can’t emphasize
enough the value of true dietary balance, eating primarily whole and real
foods, and aligning your intake with your caloric needs), but before you banish
a food from your eating repertoire, be sure you have all the facts and aren’t
eliminating something on unfounded fear.
So are lectin-containing foods
such as whole grains and legumes as dangerous to our health as proponents of
certain diets purport? Do they really cause the terrible-sounding leaky gut syndrome?
While this post won’t be a completely comprehensive discussion of lectins (I do
want you to read this, after all), my hope is that I can help provide factual information, clear up some confusion, and, with any luck, silence the
hysteria.
What are lectins?
Lectins are
carbohydrate-binding proteins found in most plants as well as in dairy. Plant
lectins are most abundant in plant seeds but are also found in other tissues
such as roots, leaves, bark, flowers, or bulbs. It has been surmised that
lectins play a defensive role in plants by protecting the plant against attacks
from microorganisms, pests, and insects. As an example of this mechanism, it
has been noted that an infection or wounding of a plant increases lectin
concentration. Within animals, lectins facilitate cell-to-cell contact, which,
as will be discussed later, can prove both positive and negative.
Lectins are found in a
wide range of commonly-consumed foods such as tomatoes, beans, peas, wheat
germ, rice, corn, garlic, avocado, leek, cabbage, tea, parsley, oregano,
spices, bean sprouts, carrots, green beans, white mushrooms, cantaloupe,
cherries, raspberries, blackberries, and roasted peanuts. From this listing, it
is clear that exposure to lectins is a frequent occurrence for most people.
What are lectins capable of doing in the body?
In high doses, lectins can
indeed be toxic. Consider the fairly well-known example of red kidney beans, which
can cause a type of “food poisoning” (with resultant vomiting, cramping, and
diarrhea) if consumed in the raw state or if improperly prepared.
In animals injected with
high levels of lectins, a variety of suboptimal health occurrences have been
observed. For example, absorbed lectins can impact distant organs, promoting
such conditions as pancreatic growth or atrophy of the thymus.
When given to experimental
animals orally, high levels of lectins can interact with gastrointestinal
mucosa, triggering acute GI distress symptoms (as in the case with raw red kidney
beans), as well as other negative effects. Because lectins have a high
resistance to proteolysis and are stable over a wide pH range, they can survive
the acidic, enzyme-containing stomach and therefore make the entire journey
from mouth to colon mostly intact and biologically active. This has been made
clear with the finding of intact lectins in human feces.
Since lectins do survive
digestion and are uniquely capable of binding to cell receptors on the gut
wall and elsewhere, our bodies may produce antibodies to them or, on the other hand, may induce
tolerance. If the body’s defenses do gear up to attack the “invading”
substances, a more widespread immune response can result. This has led to
speculation that lectins could be involved in autoimmune diseases such as type
1 diabetes or rheumatoid arthritis.
With a substantial
proportion of the lectin molecule intact in the gut, lectins are able to bind
to cells lining the digestive tract, which can lead to direct membrane damage or can indirectly affect intestinal bacterial flora. In the case of the former,
the reaction between lectins and cell membranes is believed to alter cell
function in one way or another, producing adverse effects. For instance, the
binding of lectins to liver cells in diabetic rats appears to contribute to
clumping, deformity, or permeability of cells.
Binding of lectins to gut
epithelium can also lead to brush border disruption, perpetuating a reduced
absorption of nutrients secondary to a decreased absorptive surface area.
There is also word floating around that lectins from legumes are causing obesity, by means of leptin (a hormone which regulates food intake and body weight) resistance; however, the only available information I found on this was one medical hypothesis presentation (not a study).
Equally as important to
point out when discussing lectin activity is that lectins may just as easily arrive in the gut intact and NOT
bind to mucosa, in which case there is typically little or no harmful effect
induced. What corresponding factors must be present for lectin-induced damage
to occur is still not clear, though lectin studies with rodents done to date
have provided some more insight.
It’s not clear in what circumstances ingested lectins
cause damage
In experimental rodents,
lectin activity and the potential for subsequent toxicity is influenced by the
degree and type of bacterial growth in the intestine, and studies
suggest that certain microorganisims in the gut may even be lectin-facilitating.
Another observation from a
study of excised rat GI tract segments treated with lectins points to the
idea that lectins may only prove toxic when GI tract cells have been
exposed to prior mechanical stress, as lectins can potently block repair, thus increasing membrane disruption.
As with most any dietary
element, dose and context seem to make a huge difference in regards to lectins,
and I feel it is crucial to insert a reminder here that the amount of lectin
necessary to produce most of the adverse effects seen in rodent studies is
significantly higher than the amount that would be consumed in a typical human
diet.
The mechanistic factors
which dictate the fate of ingested lectin are not completely understood.
Whether lectins will cause harm may be dependent on the overall diet history
and composition of the diet, as well as the condition of the gut flora, among
other factors. Research is still ongoing to determine both the dose and
the environment in which lectins produce unfavorable outcomes
Leaky gut syndrome and...lectins?
As alluded to in the
introductory section, lectins in whole grains and legumes are often cited as
being causative agents of a Loch Ness Monster-esque condition called leaky gut
syndrome. Because fear of developing leaky gut syndrome often lends itself to
the avoidance of whole grains and legumes, I thought it would be wise to dig
into what we know about the leaky gut syndrome phenomenon and separate the fact
from the flimsy extrapolation.
What is leaky gut syndrome?
While not officially recognized yet in the medical community, leaky gut
syndrome is said to encompass a wide range of symptoms including gas, bloating,
sensitivities to foods, cramps, skin conditions (eczema, hives, psoriasis), as
well as aches and pains. Additionally, leaky gut syndrome has been blamed for a
variety of disorders including chronic fatigue syndrome, fibromyalgia,
allergies, and depression. It isn’t clear how many people claim to have this
condition.
In reality, leaky gut
syndrome is still a medical mystery—a very gray area—to doctors, who ascertain
that presentation of leaky gut syndrome symptoms usually indicates that
there is another diagnosis that needs to be made.
What causes leaky gut
syndrome? The proposed theory is that increased intestinal permeability secondary
to damage of the intestinal lining, leads to this condition. It is further
surmised that a compromised intestinal barrier then lends noxious contents
(bacteria, incompletely digested proteins, etc) access to various internal
sites and circulation, potentially triggering an autoimmune reaction.
As might be expected,
lectins are often too easily implicated by some as causing leaky gut syndrome, since they do have
the ability in some cases to cause intestinal damage; however, this allegation of cause-and-effect is merely inference and has not been proven.
Even in more well-known
disease conditions such as inflammatory bowel disease (IBD), Crohn’s disease,
celiac disease, and irritable bowel syndrome (IBS), the question remains as to
whether a compromised intestinal barrier is part of the cause of disease, or is
the resulting effect. To date, studies investigating associations between a
leaky gut and certain disease states have only been correlative.
Since both human and mouse
studies indicate that intestinal barrier loss alone, regardless of cause, does
not necessitate disease in otherwise healthy people, it’s not certain what
could or should be done with someone who presents with increased intestinal
permeability in the absence of other diseases such as IBD or Crohn’s disease.
Also, it’s pertinent to point out that all intestinal permeability is not bad,
as permeability confers functions such as supporting nutrient and water
absorption.
As of right now, evidence
for how to best medically treat leaky gut syndrome is not there—so be warned of
anyone who professes to have such an answer. Some alternative medicine
practitioners claim that restoring gut barriers will cure underlying disease,
but this has not been proven in clinical studies. Additionally, some of these same
practitioners are recommending unsubstantiated dietary supplements to cure leaky gut syndrome, so hang on
tightly to your wallet.
Now, if symptoms ascribed to
leaky gut syndrome are, in fact, being caused by Crohn’s or celiac disease, for
example, treating these conditions should resolve the issue. Of course, it is important
to consult with your physician—digestive disorders are no joke, and appropriate
treatment often resides outside of mere diet modifications.
Should you be concerned about lectins from normal
consumption?
The lectins consumed in
normal human diets do not seem to be harmful. As evidenced by the many people
who eat and tolerate them, the majority of lectins ingested by humans appear to
reach the gut without provocation, or if they do interact, do so in a harmless
or even beneficial way. As previously mentioned, much of the research done with
lectins involves artificially high doses, which do not correspond to typical
human intakes. More research is needed to determine what effect lectins have at
normally-consumed levels in the human diet, as there have been zero long-term
studies in healthy individuals examining the effects of this.
Moreover, while there’s a
lot of noise about the potential downsides of lectins, they can be beneficial,
too. The body uses lectins for cell-to-cell adherence, inflammatory modulation,
and programmed cell death. There may also be supplementary advantageous uses for
lectins at non-toxic doses, with research being carried out in the areas of gut
regrowth following total parenteral nutrition as well as in anti-cancer
therapies.
Additional thoughts and tips before we conclude
Since the following
assertion is inescapable in discussions pertaining to eating whole grains and
legumes, lectins, and leaky gut syndrome, I might as well throw in my two cents
now. I’m pretty sure some of you are thinking, “But we weren’t meant to eat
grains or legumes! The toxins and anti-nutrients they contain are proof that
they don’t WANT to be eaten!” From an evolutionary standpoint, we may very well
not yet be fully adapted to eating grains and legumes. Keep in mind that at
some point, humans weren’t adapted to (and many still aren’t) drinking
lactose-containing milk from other mammals, but that doesn’t make milk a
non-nutritious food that definitively needs to be avoided.
Furthermore, it’s
my view that we weren’t “meant” to do a lot of things that we do today (were
you meant to be reading this post on your iPhone in an airplane at 50,000 feet above the earth? was the human body meant to sit
on its butt at a desk job everyday? were we meant to eat fatty grain-fed feedlot
meat? were people living in the northern latitudes of Minnesota meant to be
slathering coconut oil on every morsel of food that touches their lips?), yet
we do, because we now live in 2013, not in the Paleolithic era.
And as for
grains and legumes not wanting to be eaten—please
show me an animal that wants to be
eaten and maybe I’ll reconsider that argument. Anyway, my take here is that we
have these food sources available, they can be a nutritious part of a healthy
diet, and are enjoyable to eat, so why not?
Additionally, what Paleo diet proponents
and others who shun grains and legumes frequently overlook is the fact that
traditional processing of these foods greatly reduce or eliminate lectins.
Soaking, fermenting, sprouting, and cooking grains and legumes are all
techniques that will deactivate, thereby decreasing, lectins. While
fermentation and sprouting generally destroy lectins more efficiently, the two most
common techniques for whole grain and legume processing, soaking followed by
cooking, will also degrade a good proportion of lectins. Raw red kidney beans
can contain up to 70,000 lectin (hemagglutinating) units but through overnight
soaking and proper cooking (boiling for at least 10 minutes), lectins can be
reduced to safe levels. It is estimated that fully cooked beans contain around
300 lectin units.
My conclusions
With the evidence available
at this time, the mere presence of lectins found in plant foods should not be
used as a reason to avoid whole grains and legumes. In the many studies I read on this topic, despite
potential negative actions of lectin, the consensus among researchers is that
ingestion of lectin at levels after processing is unlikely to pose a risk to
human health in otherwise healthy individuals.
While there is plenty of scientific
literature (largely in observational but also in controlled studies) associating
legume and whole grain consumption with health benefits, what is reliably
missing, is research showing detrimental effects of normal consumption of whole
grains and legumes. Though it is observational, it’s still valuable to mention
that diets in the “Blue Zones,” where some of the longest-living people reside,
are very plant-heavy—including beans and grains as a staple.
I see no reason to avoid whole
grains or beans based on the potential of lectins to cause harm, or the very
elusive possibility of getting the even more elusive leaky gut syndrome, if you
are able to tolerate these foods and enjoy them. Diets that prohibit whole
grain and legume intake without substantive evidence to do so seem absurd.
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