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what is?


Medicine loves acronyms. You've heard about IBS (irritable bowel syndrome) and GERD (gastroesophageal reflux disorder). Now there's SIBO, or small intestinal bacterial overgrowth. The symptoms are very similar to those of IBS, and include diarrhea, cramping, and gas. Because the symptoms are nonspecific, diagnosing SIBO is challenging. Unlike diseases that are diagnosed by endoscopies where the doctor can actually “see” the inflammation, IBS is a disease that is diagnosed by ruling out other disorders. Physiologically, there's nothing wrong that appears in any test results, but 10-15% of the U.S. population has it, so physicians know it exists. SIBO is also not so easy to diagnose or treat.


Biology 101

Let's start with basic physiology. The stomach is connected to the small intestine, which is connected to the large intestine (often called the colon) by a muscle that is called the ileocecal valve. Inside these slippery tubes, reside billions of bacteria that researchers are finding have an integral role in disease states; specifically our immune system that captains our health and well- being.

Research is finding that all gut bacteria supports the health of the GI tract but the bacteria that reside in the small intestine are different than the ones that hang out in the large intestine. Absorption of nutrients occurs in the small intestine, so it’s always jumping with activity. Because of this, bacteria counts are naturally lower in this

organ. There is a wave called the migrating motor complex (MMC) that shimmies through the small intestine between meals. It sweeps through at 90-minute intervals to move food by-products, waste, and bacteria along.


There are ten times as many bacteria in the colon versus the small intestine.  Their job is to ferment carbohydrates. Bacteria proliferate more here because of its relatively low motility. I liken the two intestinal systems to the geographic north and south. We in the north seem to be on the run much more than the slower paced southern states!


The body has incredible ways of trying to keep a balance between the small intestine and large intestine. Structurally, the ileocecal valve maintains a one-way flow of contents; preventing back flow of the colon contents, including bacteria, into the small intestine. The stomach acids and low pH, as well as pancreatic and biliary secretions, also help to keep bacterial growth in the small intestine low. But, when the bacterial counts exceed normal values in the small intestine, adverse effects such as diarrhea, bloating, and abdominal pain. The bacteria can damage the mucosal lining, so malabsorption can occur. Hence, the diarrhea.

Ready for more physiology? Simultaneously, the liver secretes bile acids while the pancreas secretes digestive enzymes into the small intestine. These two work in conjunction with one another to break down fat in foods so the body can use, or store, fats as energy. When this eco- system is disrupted, undigested fats move into the large intestine and wreak havoc. Doctors can test your stool and measure the amount of fats. Fatty stool is technically called “steatorrhea.” Over time, SIBO can lead to deficiencies in vitamins that include B12, A, D, and E. Some people with SIBO may have a hard time digesting milk. That's because the lactase enzyme that breaks down the sugar (lactose) in milk may be destroyed by bacteria. When undigested lactose enters the colon, it leads to gas, bloating, and diarrhea.


What are some of the causes of SIBO?

  • Neurologic and muscular diseases that interfere with motility: Diabetic neuropathy and narcotics can lead to delayed stomach emptying, which in turn can lead to a longer time in the GI tract. The presence of diverticula (out pouches) in the gut also causes pooling of bacteria that proliferate.

  • Gastric pH: Stomach acids help to maintain a low bacterium count in the small intestine. When people are on proton pump inhibitors (drugs commonly referred to as PPIs) for GERD, the stomach acids are diminished. The pH increases, affecting the bacteria balance in the duodenum (the first part of the small intestine that connects to the stomach).

  • Anything that changes the natural structure of the intestines can affect SIBO. This includes surgical procedures that involve intestinal repairs, like loss of the ileocecal valve, adhesions, obstructions, or strictures.


Diagnosing SIBO

The most common method of diagnosis is hydrogen breath testing. An individual consumes a single dose of a sugar: glucose or lactulose. These sugars (AKA carbohydrates) get metabolized by the gut bacteria, and will produce hydrogen as a byproduct. This gas is expelled by the lungs and is measured in one’s breath. If there were a lot of bacteria in the small intestine, then one would expect the breath test results to be abnormally elevated. This isn't a perfect test as circumstances can affect results. If the carbohydrates are absorbed too quickly in the first part of the small intestine, then bacterial overgrowth won't be detected in the lower part of the small intestine.


Treating SIBO

Getting rid of the bacteria is first and foremost, and antibiotics are used to reduce the bacterial overgrowth. Rifaximin is one commonly used drug. It is given three times a day for a two-week period. Often times, the breath tests are repeated if symptoms still occur even after treatment with antibiotics. Reevaluating the chronic use of PPI's may also help. Remember, low acids in the stomach mean more bacteria in the small intestine. Perhaps consider more of a commitment to lifestyle and diet changes as a means to ameliorate GERD symptoms. Also, modifying one's diet to reduce some of the fermentable carbohydrates like lactose and fats may help. Many people have good results with following a low FODMAP diet. Keep in mind, that often times, SIBO cannot be treated; especially when surgery has altered the physiology of the intestines.


For people with SIBO, it’s also best not to eat meals too close together. This (fasting) practice will allow the MMC to sweep through the intestines and move the bacteria along. It’s important to ensure an adequate intake of fiber and fluids if one is suffering from constipation. The use of probiotics is still up in the air with SIBO. Some believe that they add fuel to the fire. Always check with your physician before taking them. 

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