SIBO (Small Intestine Bacterial Overgrowth)

Your small intestine shouldn’t have all that much bacteria in it, relative to your large intestine. If you end up either with too much in there, or some of the bacteria from your large intestine crawl up into the small intestine, you end up with SIBO.

The bacteria that cause SIBO aren’t technically “bad”… there’s just too much of them, or they’re in the wrong place. Part of the reason this causes a problem is because bacteria’s job (in part) is to help us break down the waste left over from our food after we extract all the good stuff. But we extract most of that good stuff in the first part of the small intestine. If the bacteria that shouldn’t get to the food particles until much later show up early to the party, they get first dibs… which can mean 1) nutrient deficiencies, and 2) lots of gas and bloating very quickly after eating (either after eating almost anything, or most notably after eating fermentable carbohydrates.)

Causes of SIBO:

Unfortunately we don’t know for sure what causes SIBO. But there are a few theories:

• Decreased gut motility. The slower food moves through your gut, the more easily bacteria in the colon will be able to crawl upstream, as it were. At least that’s one theory. I will certainly say patients who have gastroparesis often also have SIBO. I also see this in patients who have had bowel surgeries.
• Hypothyroidism will also slow down bowel transit and that can be a predisposing factor.
• Wiping out the good guys. Your microbiome is the immune system of your gut, and it is your first line of defense against both pathogenic and opportunistic bacteria that can cause you problems. Lots of antibiotics will lead to flora imbalance (dysbiosis). Proton Pump Inhibitors (PPIs) are actually antifungals, and these can do it too.
• Stress. I know, I know: stress causes everything. And it’s true: whatever your weak link is, is likely to snap when you’re under a lot of stress. But specifically, stress means you’re in “fight-or-flight” mode, and that means less blood flow to your gut (i.e. decreased release of pancreatic enzymes and HCl and bile to help you break down your food, and decreased gut motility) while it instead sends blood to your limbs to help you fight or flee from the perceived danger. So, stress can led to decreased gut motility, which can mean bacteria might have more of an opportunity to crawl upstream.

Signs and Symptoms of SIBO:

• Do you often feel gassy after meals?
• Do you have constipation, diarrhea, or alternation of both?
• Do you feel full after just eating a few bites of food?
• Do probiotics containing inulin or FOS make you gassy?
• Does fiber actually make your constipation worse? (Caveat to this: psyllium has an opposite effect of increasing constipation on about 30% of the population. But if fiber in general has a constipating effect on you, this could be an indication of SIBO.)
• Do your symptoms tend to improve when you take antibiotics?
• Do you have a hard time getting your iron levels up, but haven’t ever found a reason for it? (The bacteria themselves can consume some of the iron, accounting for this.)
• Have you had a hard time digesting fats? (These can interfere with bile, which is necessary for the absorption of fat.)
• Do you have acid reflux? (This is because HCl serves as an antibiotic in the stomach, and if it is low, as it often is in acid reflux, this can be one of the causes of SIBO. For this reason, prolonged PPI use can set you up for this too.)
• Do you have excessive belching?
• Do you have increased intestinal permeability (i.e. lots of food allergies?)

Testing for SIBO:

The small intestine is really hard to reach; endoscopies only reach the upper portion of the SI and colonoscopies only reach the bottom portion, leaving a good 17 feet of the SI that we can’t see without surgery. For that reason, the best way to go is a breath test.

The bacteria that cause SIBO release hydrogen—and in some cases, the hydrogen released can feed a prokaryotic organism called archaea which then releases methane. So in order to determine whether these organisms are present, you ingest a form of sugar (lactulose is my preference, since humans can’t digest it—only bacteria can, but some practitioners use glucose), and then you breathe into a test tube every 20 minutes for three hours. The levels of hydrogen and/or methane produced will determine the diagnosis.

Treatment for SIBO:

The pharmaceutical treatment for SIBO is a bacteriostatic antibiotic called Rifaximin if only hydrogen is high, and Rifaximin and Neomycin both if methane is also high. Both antibiotics are very targeted (not likely to cause the kind of fallout of the broad-spectrum antibiotics), and also poorly absorbed, so they tend to stay in the gut.

The up side: patients who have SIBO and take these meds tend to feel much better quickly.

The down side: relapse is very common, and Rifaximin is expensive (as it’s still under patent). In my experience, several rounds are usually necessary. Sometimes after the antibiotics we will move on to natural antibiotics for maintenance, and it is also necessary to maintain a fairly strict diet that is low in fermentable carbohydrates. (For this I prefer the Specific Carbohydrate Diet, but I do have some patients who have SIBO and do better on the FODMAPs diet instead.)

Have I seen people get completely better? Absolutely. But I will also say that most SIBO success cases have also been those where the apparent underlying cause has been identified and corrected.