FOUL!
Scientists Uncover Sickening Properties of Undercooked Beans, Rice
People cry foul when fowl is undercooked, but
what about red beans and rice?
Scientists have discovered how lectins, a family of proteins believed to be a natural insecticide abundant in undercooked legumes and grains, can make you temporarily miserable.
“It’s known that it can be a toxin,” Dr. Paul L. McNeil, an MCG cell biologist, said of the lectin protein commonly found in vegetables. Lectins, which bind strongly to carbohydrates on cell surfaces, have a particular affinity for the heavy-carbohydrate coats of epithelial cells that line the gastrointestinal tract.
Researchers have long known that undercooked lectin can cause nausea, diarrhea and vomiting, but they didn’t know how.
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,” said Dr. McNeil. “That means you have gaps in the integrity of the surface area of the epithelium, exposing the nasty internal world of your GI tract to your blood supply.”
The epithelial lining continually blocks digesting food in the GI tract from the blood supply. When intact, it allows only good things 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,” said 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. And you are not going to eat red beans again the next day. That is probably the point if they are natural insecticides.”
Dr. McNeil, who first identified how injured cells patch themselves, said lectin blocks the repair mechanism better than anything else he’s seen. He and his colleagues showed in PloS Biology in 2006 how roughage—which includes beans—helps 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.
“It might tell us more about the mechanism of repair,” said Dr. McNeil. “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 well. It’s a very rapid, surface-initiated inhibition.”
Lectin has also been linked to colorectal cancer and celiac disease, which prevents proper nutrient absorption after ingesting gluten. A recent Science paper implicated lectin in diabetes as well.
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 said.
“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 said, 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 noted that although lectin is easily among the top- 10 causes of food poisoning, it 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.
--Toni Baker