01/29/2013 08:12 am ET Updated Jan 29, 2013

Urban Legends Of Your Digestive Tract

By Tamara Duker Freuman for U.S. News

We all love a good urban legend, and it can be especially fun when they turn out to be true.

It recently dawned on me how many urban legends out there deal specifically with digestion, and I decided to take on three of the most interesting ones.

The shrouds of secrecy under which our digestive inner workings take place make them especially prone to musings and myths of all sorts. People give little thought to the machinations of their GI tract, and most of us take for granted that what goes in will eventually come out. But despite the remarkable efficacy of a well-functioning digestive system -- the stomach's acidity, the multi-pronged attack of digestive enzymes in the bowel, and the powerful squeezing and churning of smooth muscle throughout the gut -- sometimes, food or medicine can get stuck along the way.

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Indeed, many of the digestive urban legends I've come across deal precisely with the issue of obstructions, which are blockages somewhere along the GI tract. Obstructions can be partial or complete, and in adults, they are generally caused by abnormally slow stomach emptying or other problems with GI motility, scar tissue from nearby surgeries, inflammation, or undigested food or medicines.

If a ball of undigested material causes the blockage, it is called a "bezoar." Symptoms of an obstruction include vomiting, lack of bowel movements or inability to pass intestinal gas, and abdominal pain.

So without further ado, behold the following list of urban legends, divided into verified urban truths and discredited urban myths.

1. Urban Truth: Coca-Cola Is An Effective Treatment To Dissolve Certain Gastric Blockages
Coca-Cola has a very low pH level (around 2.5 to 2.6, which is among the lowest of all carbonated soft drinks). It is believed that Coca-Cola's acidity, coupled with its carbon dioxide content (from the carbonation) are two main factors that enable it to dissolve various types of organic matter -- including undigested plant fibers that get stuck as they attempt to exit the stomach. These hard masses of plant material that form obstructions in the stomach are known as gastric "phytobezoars."

Recent research out of Greece has been making sensational headlines for its endorsement of using Coca-Cola as a first-line treatment to dissolve these gastric phytobezoars. But in reality, this research isn't new news; the scientific literature offers dozens of case reports documenting the successful treatment of various bezoars with Coke, and your gastroenterologist may even have a few carbonated war stories of his own.

An elderly patient with gastroparesis -- a common condition in which stomach emptying time is abnormally delayed -- was once treated with Coca-Cola for a phytobezoar by a doctor in my New York-based practice. For three days, her physician ran Coca-Cola straight into her digestive tract via a nasal tube at a rate of about one can per hour. When all was said and done, there was complete and total dissolution of her bezoar blockage. The only side effect? She was bouncing off the walls from all that caffeine and sugar!

2. Urban Truth: Eating Persimmons Can Cause Blockages, Even In Healthy People
Persimmons are a beautiful coral-colored fruit that resemble tomatoes in appearance. They are more common in Asian diets than typical Western ones, though persimmon pudding is a regional treat popular in the Midwest.

Oddly, unripe persimmons contain a natural compound that can form a glue-like substance when combined with acid (such as stomach acid); the hard masses that result are reportedly the leading cause of plant-related bezoars globally! Unlike a typical phytobezoar, which is far more likely to affect someone with an underlying medical condition like gastroparesis, persimmon bezoars can affect healthy people with normal digestive function as well.

They are so common, in fact, that there is a special medical term dedicated entirely to them: diospyrobezoars. An even more interesting piece of obstruction-related trivia: Coca-Cola is not nearly as effective at dissolving persimmon bezoars because they are generally much harder than the standard, run-of-the-mill phytobezoar made of regular old plant fibers.

3. Urban Myth: Swallowed Gum Does Not Build Up In The Stomach For "Seven Years" (Or At All)

As children, we've all been on the receiving end of a dire warning from our mothers, our babysitters, or anyone else trying to deter us from swallowing our chewing gum. Swallowed wads of gum, we were cautioned, would sit in our stomach for seven years. Frightening prospect! But is it true?

No, it is not. The scientific literature is pretty quiet on reported cases of chewing gum as the cause of GI obstructions, and for good reason. Chewing gum is essentially latex -- a natural, protein-containing emulsion derived from certain species of trees. When gum arrives in the acidic stomach environment, the proteins in the latex become denatured -- or broken down in a way that collapses their shape, just like any other dietary protein would be. As a result of this process, the residual portion of the swallowed gum wad gets stiff and very small such that it can easily pass out of the stomach, through the intestines, and out the back door.

Now, all this talk about obstructions isn't meant to scare anyone off of eating fibrous fruits and veggies -- nor is it intended to encourage recreational chewing-gum swallowing. While the scientific literature is rife with isolated case reports of bezoars caused by random foods (pomegranate seeds, dried apricots, and whole okra pods, for example), the fact is that most of these cases involve people who have eaten a wildly extreme or abnormally large amount of the food in question.

Obstructions are quite uncommon in healthy people, though there are certainly risk factors of which to be aware.

As suggested above, having delayed stomach emptying -- which is a common side effect of long-term diabetes -- is the most likely factor to predispose someone to a gastric bezoar. And a history of abdominal or pelvic surgery (including weight-loss surgeries) in which scar tissue may have formed in or around the intestines can increase the chances of an obstruction further downstream in the intestines.

Other medical conditions that could increase one's risk of a GI obstruction include Cystic Fibrosis, Sjogren's syndrome, pancreatic insufficiency, and Crohn's disease. If you have a medical condition that predisposes you to obstructions of any kind, make an appointment to see your friendly, local dietitian for recommendations regarding which foods and supplements you may want to limit or avoid altogether.