Celiac Disease and Small Intestinal Bacterial Overgrowth

When you're first diagnosed with celiac disease, you likely hope—and anticipate—that the gluten-free diet will solve your digestive problems. However, studies and anecdotal evidence indicate it's not always that easy. In fact, a significant percentage of people with celiac disease continue to experience symptoms even after going gluten-free.

There are several potential reasons for these ongoing digestive symptoms, all of which you can have in addition to celiac disease: gastrointestinal reflux disease (GERD), irritable bowel syndrome (IBS), and inflammatory bowel disease (IBD). Also, other mostly non-digestive conditions found in people with celiac disease, such as thyroid disease, can cause digestive symptoms.

Refractory celiac disease (celiac disease that doesn't improve despite the gluten-free diet) also can cause continuing symptoms, although it's very rare. And of course, accidentally eating gluten—even tiny amounts of gluten—can lead to a nasty reaction. That's unfortunately quite common.

But one possible explanation for continuing symptoms that may sometimes fly under the radar is small intestinal bacterial overgrowth (SIBO). SIBO can cause diarrhea, abdominal pain, and bloating along with nausea and excessive gas. Does that sound like your symptoms? If so, read on.

What Is SIBO?

Everyone's digestive system includes bacteria... lots of bacteria. These trillions of tiny organisms, most of which are found in your large intestine, help you digest your food and even produce vitamins, such as vitamin K and biotin.

Your small intestine also hosts bacteria, but different varieties and in far smaller amounts than your large intestine. SIBO occurs when bacteria that normally live mainly in your large intestine move upstream to your small intestine and multiply.

When those bacteria grow where they shouldn't, they can cause all kinds of digestive symptoms, and in the most severe cases, SIBO can result in deficiencies of vitamins and nutrients. SIBO is difficult to diagnose properly, and people's symptoms don't always respond well to treatment.

SIBO and Celiac: What's the Connection?

As you probably know, celiac disease occurs when your body's immune system reacts mistakenly to the protein gluten, found in the grains wheat, barley, and rye. When someone with celiac ingests gluten, their white blood cells attack the lining of their small intestine, leading to what's called villous atrophy. Even though celiac disease stems from your digestive system, it affects your entire body, creating symptoms everywhere from your digestive tract to your brain and your skin.

Meanwhile, SIBO's symptoms mimic the digestive symptoms of celiac disease almost perfectly. SIBO symptoms include digestive problems such as heartburn, diarrhea, gas, bloating, and abdominal pain. Particularly severe SIBO can lead to fatigue and weight loss. Any of these symptoms also can be seen in undiagnosed celiac disease as your body's immune system destroys the small intestinal lining.

In fact, SIBO actually can cause villous atrophy, the small intestinal damage typically seen in those with celiac disease. So how can you tell the two conditions apart?

To diagnose celiac disease, healthcare providers usually use blood tests to look for specific markers that indicate your body's reaction to the gluten protein. These tests, plus a medical procedure called an endoscopy that allows your practitioner to look directly at your small intestinal lining, can definitively identify celiac disease.

SIBO, meanwhile, is diagnosed through a breath test, although healthcare providers also can use endoscopies. To make matters even more complicated, there's some evidence that the breath test may not work all that well to diagnose SIBO in people with celiac disease.

You Can Have Both SIBO and Celiac Disease

It's possible to have both celiac disease and SIBO at the same time, which makes telling their symptoms apart even more difficult. In fact, some research shows that SIBO may be more common than average in people with celiac disease, especially in people whose digestive symptoms don't improve on the gluten-free diet. However, other researchers have cast doubt on that conclusion.

One review of the medical literature on SIBO and celiac disease, which included 11 different studies, found that one-fifth of people with celiac also had SIBO.

That review found that 28 percent of those with celiac disease who continued to have symptoms despite following the gluten-free diet carefully also had been diagnosed with SIBO. Meanwhile, only 10 percent of those with celiac whose symptoms cleared up on the gluten-free diet were diagnosed with SIBO.

Still, even as medical researchers explore how many people with celiac may also have SIBO, it's not clear why the risk may be higher. One possible explanation involves intestinal motility, which is the movement of food through your digestive tract. People with celiac disease may have faster-than-normal or slower-than-normal motility, or sometimes even have slower-than-normal motility in part of their digestive tract (for example, in the stomach) combined with faster-than-normal motility in another part (for example, in the colon). Problems with intestinal motility could lead bacteria to grow where they shouldn't.

A Word From Verywell

If you've been diagnosed with SIBO, your healthcare provider most likely will prescribe a specific type of antibiotic called rifaximin. This antibiotic, which also is used to treat traveler's diarrhea (caused by bad bacteria in your digestive tract), isn't absorbed well by the body, which means it works almost exclusively in your digestive tract.

However, SIBO need not be treated with rifaximin exclusively (other treatments exist), and not everyone sees relief from antibiotic treatment. One study found that people with celiac disease who were diagnosed with SIBO and then treated with rifaximin didn't see any improvement in their digestive symptoms from the antibiotic. That study included 25 people with celiac who took the antibiotic and compared them with 25 people with celiac who took a placebo.

SIBO isn't well understood yet, so it's difficult to identify and treat people who may have it. As time goes on, we should have more information on what works in SIBO and what doesn't, which will help everyone, including those who have both SIBO and celiac disease.