"Are Lectins in Food Good or Bad For You?"
Lectins are to blame for the great “white kidney bean incident”
of 2006 in Japan.
One Saturday evening, a TV program introduced a new method to lose weight.
The method was simple: toast some dry raw white kidney beans
in a frying pan for 3 minutes, grind the beans to a powder,
and then dust it on their rice.
Within days, a thousand people fell ill,
some with such severe diarrhea and vomiting they ended up in the hospital.
Why?
Lectin poisoning.
Three minutes of dry heat is not enough to destroy
the toxic lectins in kidney beans.
If you don’t presoak them, you need to boil large kidney beans
for a full hour to completely destroy all the lectins,
though if you first soak them over night,
98% of the lectins are gone after boiling for just 15 minutes,
and all gone by half an hour.
And indeed, when they tested the white beans,
toasting for 3 minutes didn’t do a thing—
no wonder people got sick--
whereas 95% of the lectins were inactivated
after boiling them for three minutes, and completely inactivated after 10.
Evidently, “Do not eat raw beans” is a traditional admonition in Japan
to avoid intestinal problems, and now we know why.
While canning may completely eliminate lectins from most canned beans,
some residual lectin activity may remain in canned kidney beans,
though apparently not enough to result in toxicity.
And ironically, low doses of lectins may be beneficial
by stimulating gut function, limiting tumor growth, and ameliorating obesity.
What?
I thought lectins were toxic.
For as long as people have speculated dietary lectins are harmful,
others have conjectured that they may be protective.
If this theory is correct, appropriate lectins by mouth should be of use
in the prevention (and possibly treatment) of colon cancer.
Or, of course, we could just eat our vegetables.
Interest in the purported anti-tumor effect of plant lectins started
with the discovery in 1963 that lectins could distinguish
between cancer cells and normal cells.
Researchers at Massachusetts General found a substance in wheat germ—
the lectin in whole wheat—which appeared to be tumor cell specific,
clumping together the tumor cells,
while the normal cells were left almost completely alone.
So specific that you can take a stool sample from someone and,
based on lectin binding to the colon lining cells
that get sloughed off into the feces,
you can effectively predict the presence of polyps and cancers.
And subsequently, it was discovered that lectins couldn’t just distinguish
between the two but also extinguish the cancer cells,
while largely leaving the normal cells alone.
For example, that same white kidney bean lectin was found
almost completely suppress the growth of human head and neck cancer cells,
liver cancer cells, breast cancer cells,
and (at least, most of the way) cervical cancer cells,
within about 3 days.
But this was in a petri dish.
That’s largely the basis of the evidence for the anti-tumor activity
of plant lectins, these petri dish studies.
How do we even know that dietary lectins are absorbed into the body?
Colorectal cancer is one thing.
The fact that lectins can kill off colon cancer cells in a petri dish
may be applicable, since lectins we eat may come in direct contact
with cancerous or precancerous cells in our colon,
providing a mechanism by which bean consumption may help
in the prevention and treatment of colorectal cancer.
Or, even more exciting is the potential
for effectively rehabilitating cancer cells.
The loss of differentiation and invasion are the hallmarks
of malignant tissues,
meaning that when a normal cell transforms into a cancer cell,
it tends to lose its specialized function.
Breast cancer cells become less breast-like;
colon cancer cells become less colon-like.
And, what these researchers showed for the first time
is that the lectin in fava beans could take colon cancer cells
and turn them back into looking more like normal cells.
Here’s the before picture, cancer cells just growing in amorphous clumps,
but then, here’s those same cancer cells after two weeks
exposed to the fava bean lectins.
The cells have started to go back to growing glandular structures
like normal colon tissue.
Therefore, dietary lectins or putting them in a pill
or something may slow the progression of colon cancers,
potentially helping to explain why dietary consumption of beans,
split peas, chickpeas, and lentils appears to reduce the risk
of colorectal cancer based on 14 studies
involving nearly two million participants.
OK, but what about cancers outside the digestive tract?
Although lectin containing foods like beans and whole grains
are frequently consumed cooked or otherwise processed,
these treatments may not always completely inactivate the lectins.
For example, lectins have been detected in roasted peanuts.
Peanuts are legumes, and we don’t tend to eat them boiled,
but just roasted or even raw.
Yeah, but are we able to absorb the lectins into our system?
Yes.
Within an hour of consumption of raw or roasted peanuts,
you can detect the peanut lectin in the bloodstream of most people.
Same thing with tomatoes.
Some of the non-toxic lectin in tomatoes
also makes it down into our gut and into our blood.
The wheat lectin known as WGA, the wheat germ agglutinin,
doesn’t seem to make it into our bloodstream though,
even after apparently eating the equivalent of more
than 80 slices of bread's worth of wheat germ.
And, if you ate something like pasta,
the boiling might wipe out the lectin in the first place anyway.
In terms of phytochemicals in the fight against cancer,
lectins are able to resist digestion, resulting in high bioavailability,
potentially allowing the cellular mechanisms of the host
to utilize the full potential of the “dramatic” anti-cancer benefits
lectins have to offer.
But, these dramatic benefits have yet to be demonstrated in people.
But look, we know that population studies show that the consumption
of a plant-based diet is strongly associated with a reduced risk
of developing certain types of cancer.
Now, they could just be eating fewer carcinogens,
but plants do have all those active components that do seem to protect
against the initiation, promotion, and progression of cancer;
and so, maybe lectins are one of those protective compounds.
Look, we know people who eat more beans and whole grains
tend to get less cancer overall;
we’re just not sure exactly why.
Now, you could say, ”Who knows, who cares?”
Well, Big Pharma cares.
You can’t make as much money on healthy foods
as you can on lectin-based drugs.