Work published Aug. 1 in PloS One shows lectins disable GI tract cells, which are constantly bombarded while  digesting food, from repairing tears in cells walls from all the activity. Repair  normally occurs in seconds: internal membranes move up to patch the tear, the  cell recovers and the one-cell layer lining of the GI tract remains intact.

"If those individual cells cannot repair tears, they die," says Dr. McNeil.  "That means you have gaps in the integrity of the surface area of the  epithelium and you are exposing the nasty internal world of your GI tract to  your blood supply."
The epithelial lining is a continuous, natural barrier between digesting  food in the GI tract and the blood supply. When intact, it allows only good  stuff like nutrients to pass through.

 "Your body senses that lack of  barrier function and tells you to eliminate the entire contents of the GI  tract," says Dr. McNeil, noting that lectin's apparent role as a natural  insecticide and as a source of food poisoning are related. "If you get vomiting  and diarrhea you are going to eliminate the entire contents of your  gastrointestinal tract, right? And, you are not going to eat red beans again  the next day, right? That is probably the point if they are natural insecticides.  Alcohol will do the same thing. When you drink too much alcohol, you can destroy  the lining of your stomach."

But the scientist who first identified how injured cells patch themselves  says lectin blocks this repair mechanism better than anything else he's  seen.  Interestingly, he and his  colleagues showed in PloS Biology in 2006  how roughage – which includes beans – help people stay "regular" by causing  more cell tears, which enables more mucus to escape from cells, essentially  greasing the GI tract.

That same research team, which  includes Dr. Katsuya Miyake, MCG cell biologist, and Dr. Toru Tanaka,  pharmacologist at Josai University in Japan, has now shown lectin is also very  good at blocking mucus expulsion from cells.

In fact, they discovered lectin's role in stopping cell-patching and mucus  release while researching roughage. The multipurpose lectin is a powerful stain  the team used to look at mucus released by cells after tearing. They found if  they used too much lectin there was no patching or mucus, just cell death.

"Biologically it's interesting  because it might tell us more about the mechanism of repair," says Dr. McNeil,  who wants to learn more about how lectin interferes with repair. "We know the  mechanism involves surface binding because you can add lectin and the cells  can't repair. You take the same culture of cells, wash the lectin away, injure  other cells in the culture and they repair fine. We also know it's a very  rapid, surface-initiated inhibition."

In addition to the immediate discomfort undercooked beans and rice can  cause, long term concerns ingestion of lectin has also been linked to  colorectal cancer and celiac disease, a common problem in which individuals are  sensitive to gluten, a mixture of proteins derived from wheat flour that  includes lectins. The small intestine of the celiac sufferer is unable to  properly absorb nutrients after gluten ingestion.

Oddly, in a laboratory dish, safe from mechanical stresses that cause  surface tears, lectin can make cells divide, "which is quite the opposite of  making cells sick," Dr. McNeil says. A recent Science paper implicated lectin in diabetes as well.

"It's possible that this bioactive property of lectin that binds to our  cells could have long-term consequences taken even in small amounts," he says,  noting that thorough cooking destroys most but not all lectin. "Maybe the  bloating and gas is telling us something about lectin when it's just a minor  irritation."

He notes lectin is easily among the  top-10 causes of food poisoning but is unlikely to be lethal because the body  is so good at sensing the break in the GI barrier and eliminating the problem.

The research was funded by NASA.

www.plosone.org/doi/pone.000687.