SIBO: A Four-Letter Word for Bloating

While it's normal -- and indeed essential to health -- to have large populations of bacteria living in our colon, it's not normal to have such large populations living further upstream in the small intestine. When gut bacteria do manage to take hold and form larger-than-normal colonies in the small intestines, it results in Small Intestinal Bacterial Overgrowth, often referred to as SIBO, or just plain "overgrowth." SIBO is associated with all manners of digestive misery -- including abdominal bloating and distension, discomfort/tightness soon after eating, excess belching, excess flatulence, nausea and diarrhea -- though some people predisposed to constipation can experience this, too. In some cases, symptoms become so severe that people are unable to work, travel and go about their normal lives.

[Read: Low FODMAP Diet -- What You Need to Know .]

The symptoms of SIBO largely result from the fermentation festival that bacterial colonies stage in the small bowel once they settle in there. Since bacteria typically feast on carbohydrates and produce gas and other irritating metabolic byproducts as a byproduct of their efforts, a variety of dietary carbs can make symptoms of SIBO worse -- such as fructose and sorbitol in fruits, lactose in dairy, fructans in wheat or onions, and more complex fibers in beans and broccoli. Indeed, the more easily fermentable the carbs, the more suffering they are likely to produce -- even if the foods they're found in are objectively "healthy." These families of highly fermentable carbs are sometimes referred to as FODMAPs.

As the small intestine is relatively narrow, even small amounts of extra gas produced there may cause excessive pressure and result in substantial discomfort. And other byproducts of bacterial fermentation are known to be GI irritants as well. Since most people eat several times per day, those with SIBO often find themselves feeling chronically miserable, as the byproducts of fermentation are constantly being generated upstream just as the previous batch may be making its way out.

[Read: 5 Common Causes of Belly Bloat .]

SIBO can often elude diagnosis for a long time, and that's because its symptoms overlap with a variety of other common digestive conditions, such as Irritable Bowel Syndrome, acid reflux and gastroparesis (delayed stomach emptying). Furthermore, it's not visible through common diagnostic procedures like endoscopy, colonoscopy or CT scans, which means the condition can go unnoticed even among patients who get a very thorough medical workup. The most common way to diagnose SIBO is through a lengthy breath test, in which patients drink a beverage that contains a highly fermentable sugar and then breathe into a tube every 15 to 20 minutes for up to three hours so their breath gasses can be measured. Unfortunately, most doctors -- even gastroenterologists -- do not have the specialized equipment to conduct these tests.

While there's no surefire way to tell if your bloating is the result of overgrowth without the benefit of a properly-conducted breath test (or one of the other, more invasive diagnostic methods), here are some clues that raise my red flags and index of suspicion for SIBO:

-- Sudden onset of bloating and excess gassiness (either belching, flatulence or both). As in, you can pinpoint the day in which things went from fine to bad.

-- Aforementioned bloating started soon after starting an acid-reducing medication for reflux.

-- Symptoms started soon after an abdominal surgery or intestinal resection -- particularly one in which the valve separating the small and large intestines was removed, or a section of the intestine was bypassed (as in certain weight-loss surgeries).

-- You have a history of IBS or constipation, but your current symptoms are qualitatively different (and worse) than they've been in the past.

-- You feel bloated no matter what you seem to eat, and often even wake up feeling gassy and distended.

-- Symptoms are chronic. They may be relatively better or worse depending on what you eat, but they never go away.

-- Foods that you once tolerated well suddenly seem to cause significant discomfort within one hour of eating -- such as apples, juice, broccoli, beans, Fiber One cereal or sugar-free foods and beverages

-- You've experienced a sudden change in bowel habits -- either chronic diarrhea or (worsening) constipation

-- Symptoms improve or completely resolve on a very low carb or low FODMAP diet, but return as soon as you begin eating normally again.

-- Symptoms improved temporarily when you happened to have taken antibiotics for a different reason (like a sinus infection).

-- Your symptoms have not responded to the usual interventions. For example, you remain constipated despite a high-fiber diet, or your bloating and diarrhea persist despite various medications your doctor has prescribed.

-- Recent bloodwork showed you were deficient in vitamin B12, and you're not vegan.

While SIBO was once considered a relatively rare occurrence, it's on the collective radar screen of doctors to a much greater degree nowadays. When a doctor suspects you have SIBO he or she may send you for breath testing to verify the diagnosis, or he or she may go ahead and treat you with a course of antibiotics based on suspicion alone -- particularly if no facilities nearby have the appropriate equipment for testing.

[Read: How Grazing Affects Your Digestive Function .]

There are pros and cons to both approaches, and it's worth discussing these with your doctor. For example, if you're treated first without a test and your symptoms persist after a round of antibiotics, does it mean you didn't really have SIBO to begin with, or does it mean that your particular critters didn't respond to the specific antibiotic your doctor chose? In other words, would a different antibiotic be helpful, or are you barking up the wrong tree and risking unnecessary antiobiotic use? Moreover, you cannot have a breath test within four weeks of taking an antibiotic, so treating first and testing later means that if you do eventually decide to have the test, you'll have to wait at least a month to do so. On the flip side, if your doctor does prescribe antibiotics based on his or her educated hunch and you end up getting better after all, then you'll have gotten a quick and merciful resolution to the misery that SIBO often entails.

Diet has not been shown to cause SIBO, nor has it shown the potential to cure it. The most dietary remedies can do is help alleviate symptoms associated with SIBO pending medical resolution of the condition. This, however, is non-trivial; the benefit of diet interventions can be profound in terms of improving quality of life and minimizing symptoms during a bout of overgrowth. If you suspect you may have SIBO or have been struggling with a confirmed case of it, a dietitian with specific knowledge of the low FODMAP diet can help you weather the storm.

[Read: Foods That Cause Bloating .]

Tamara Duker Freuman, MS, RD, CDN, is a registered dietitian whose NYC-based clinical practice specializes in digestive disorders, celiac Disease, and food intolerances. Her personal blog,, focuses on healthy eating and gluten-free living.