Why Undercooked Red Beans and Rice can Make you Sick

Researches have uncovered how lectins, a family of proteins believed to be a natural insecticide that is abundant in undercooked legumes and grains, can make you feel temporarily poisoned.

The name “lectin” is derived from the Latin word legere, meaning “to select”.

“It’s known that it can be a toxin,” says Dr. Paul L. McNeil, cell biologist at the Medical College of Georgia. Lectin, which binds strongly to carbohydrates that decorate cell surfaces, have a particular affinity for the heavy-carbohydrate coats of epithelial cells that line the gastrointestinal tract.

Why do Certain Foods Contain Toxins?

Plants have evolved many defense strategies against herbivores, their natural predators, thorns for example. By far the most common is their chemical weaponry.


Why do Certain Foods Contain Toxins?

Plants have evolved many defense strategies against herbivores, their natural predators, thorns for example. By far the most common is their chemical weaponry.

Sweet potato, clover and soy all contain phytoestrogens, which mimic the effects of sex hormones in animals. Eating too much of these plants can mess with an animals reproductive system and render them sterile, effectively controlling the amount of herbivore predators the plants have to deal with.

Indian vetch contains a powerful neurotoxin; it can cause paralysis when consumed. Nightshades such as jimsonweed contains potent hallucinogenic alkaloids. All of these chemical weapons are effective and have evolved to benefit the survival of the plant.

Food Poisoning by Lectin

Researchers have long known that ingesting too much undercooked lectin can cause nausea, diarrhea and vomiting. What they didnt know was how lectin caused food poisoning.

Published Aug. 1 in PloS One, the study shows lectins disable GI tract cells, which are barraged 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.”

Your 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 lectins 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 hes seen. He and his associate researchers 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.

Mucus Expulsion Blocked

The same research team, has shown lectin is also good at blocking mucus expulsion from cells.

In fact, they discovered lectins 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 its 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 cant 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 its a very rapid, surface-initiated inhibition.”

Long Terms Dangers

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.

“Its 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 its 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.

photo by Carlos Lopez Creative Commons Attribution License