Small Intestinal Bacterial Overgrowth (SIBO): Do I Have It?

Medically Reviewed by Zilpah Sheikh, MD on December 11, 2023
Written by Kim Painter, Caitlin Cox
8 min read

Everyone has bacteria in their gut. They play a key part in digestion. But these bacteria live mostly in your large intestine, or colon, not your small intestine. When too many of the wrong kind of bacteria end up in the small intestine, that can cause trouble—a disorder called small intestinal bacterial overgrowth or SIBO.

The small intestine is the longest section of your digestive tract, at about 20 feet. It's where food mixes with digestive juices and where nutrients and water are absorbed into your bloodstream before waste moves to your colon. SIBO can get in the way of all that, causing digestive symptoms and other problems.

SIBO vs. blind loop syndrome

Some cases of SIBO are called blind loop syndrome because they happen when food stops moving normally through part of the small intestine. Doctors call that section a blind loop because food either goes around it or gets stuck there. But SIBO can have other causes.

SIBO vs. irritable bowel syndrome (IBS)

SIBO has many of the same symptoms as IBS, a common digestive disorder that causes constipation, diarrhea, or both, along with digestive discomfort. Studies suggest that in some cases, SIBO might be the root cause of IBS.

How common is SIBO?

Studies on people with IBS have found SIBO rates ranging from 4% to 78%. Those studies have found rates in healthy people from 1% to 40%. One problem is that different testing methods can produce widely varying results. Scientists are trying to figure out the best testing methods to find the true rates. In general, studies show higher rates in older than in younger people and links with additional conditions including inflammatory bowel disease (IBD), liver disorders, and the aftermath of stomach surgery.

SIBO may cause:

  • Belly pain
  • Queasiness
  • Bloating
  • Uncomfortable fullness after eating
  • Loss of appetite
  • Indigestion
  • Passing a lot of gas
  • Diarrhea or constipation
  • Fatigue
  • Weakness
  • Unintended weight loss
  • Malnutrition

SIBO and your poop

SIBO can change the way your poop looks, causing what doctors call steatorrhea or fatty stools. You might notice that your poop floats and is looser, smellier, and paler than usual. This can happen to anyone after a fatty meal, but if it happens a lot, it can be a sign of a medical problem. SIBO is just one possible cause, and most people with SIBO don't have this symptom, so it's important to talk to your doctor about any lasting change in your poop.

SIBO and constipation

 Most people with SIBO have diarrhea or go back and forth between diarrhea and constipation. But it is possible to have SIBO with constipation alone. When you have constipation, you don't poop as often as usual for you, and your poops may be dry, hard, and difficult to pass. The kind of bacteria overgrowing in your small intestine may cause SIBO with either mostly diarrhea or mostly constipation.

SIBO can have several different causes. Many cases stem from these issues:

Low stomach acid

When you don't have enough acid in your stomach, your body doesn't control bacterial growth as well as it should. That can lead to SIB0.

Low stomach acid can develop if you take medication such as antacids and proton pump inhibitors, commonly used for heartburn. Infections such as H. pylori, a major cause of stomach ulcers, can lower acid levels as well. Gastric bypass surgery for weight loss can also lead to low stomach acid.

Slow-moving digestion

If your small intestine doesn't move food along as quickly as it should, bacteria can grow and stick around too long. This can happen because of problems with nerves and muscles, sometimes after an illness, injury, or surgery. It also can happen if you have low levels of thyroid hormone.

Structural problems

You might have extra nooks and crannies in your small intestines where bacteria can build up. This can happen when surgery for digestive diseases creates scar tissue or partial blockages. Or you might have diverticulosis, a common condition in which pouches form in the intestines as you age.

Medication overuse

If you take antibiotics or narcotics (drugs like codeine, fentanyl, and oxycodone), they can upset the normal balance of bacteria in your gut. Narcotics also can slow your digestion.

Age is an important risk factor for SIBO because older people are more likely to have medical conditions that cause low stomach acid or slow-moving digestion. They also take more medication.

Having stomach surgery for ulcers or obesity also can increase risk, as can radiation treatments of the abdomen.

Some of the medical conditions that can increase risk include:

  • Diabetes
  • Lupus
  • Celiac disease
  • IBDs
  • IBS
  • Pancreatitis
  • Colon cancer
  • Scleroderma
  • Chronic kidney failure
  • Liver disease

Can foods trigger SIBO?

Foods don't cause SIBO, but foods that encourage harmful bacteria to keep growing can make it worse. Your doctor might recommend a special diet as part of your SIBO treatment.

Symptoms of SIBO can look like those of many other conditions. And you may have some of those conditions—such as irritable bowel disorder—along with SIBO. So diagnosis can be tricky. If you have unexplained symptoms that don't go away, see a gastroenterologist. This type of doctor specializes in the digestive system.

SIBO tests

If a doctor suspects you have SIBO, they may start by giving you a hydrogen breath test. To take this test, you drink a sugary beverage and then breathe into a tube every 15-30 minutes over a few hours. If the test shows you breathe out a high amount of hydrogen gas, that's a sign you could have SIBO. The breathing test may also look for methane, another gas linked with the overgrowth of some organisms in the small intestines.

For a more detailed look at what's in your small intestines, your doctor may do a test called a small intestine aspirate and fluid culture. To do it, the doctor passes a long, thin tube called an endoscope down your throat through your stomach to your small intestine. They take a small sample of the fluid inside and do a lab test called a culture to see what kind of bacteria or other organisms are growing.

In addition, you may get:

  • Imaging tests like as X-rays, CT, or MRI to look for physical problems in your intestines
  • Blood tests to check for anemia or a lack of vitamins
  • Stool tests that look for problems like how much fat your body is absorbing

To treat SIBO, you need to lower the amount of bacteria in your small intestines and, if possible, treat the underlying problem causing the overgrowth. You also may need treatment for any complications.

SIBO antibiotics

Antibiotics are the main treatment of bacterial overgrowth. The exact antibiotic you get might depend on the results of your breath test.

Some of the antibiotics you might get include:

  • Amoxicillin-clavulanic acid (Augmentin)
  • Ciprofloxacin (Cipro)
  • Metronidazole (Flagyl)
  • Neomycin (Mycifradin)
  • Norfloxacin (Noroxin)
  • Rifaximin (Xifaxan)
  • Trimethoprim-sulfamethoxazole (Bactrim)

You might need to take antibiotics for only 1 or 2 weeks or for a longer time. Your doctor could also switch among several kinds. You also might need to take antibiotics repeatedly if bacterial overgrowth returns. Treatment can be complicated by the fact that antibiotics disrupt the balance of bacteria throughout your digestive tract, sometimes causing some of the symptoms you are trying to treat, such as diarrhea.

Other medicines

You might also get medicines that speed up intestinal movement.

Nutritional supports

SIBO can make it so your body doesn't absorb enough of certain nutrients like vitamin B12, iron, thiamine, and niacin. Supplements may help. You might get shots of vitamin B12, as well as pills containing vitamins and minerals. Some people who get seriously malnourished might need to get liquid food through a tube in a vein for a short time.

Because damage to your small intestine can reduce your ability to digest lactose, the sugar in milk and other dairy products, you might need a lactose-free diet. If you don't have dairy foods in your diet, you'll need to get vitamin D and calcium elsewhere, from supplements or from other foods.

Surgery

Some people need surgery if their SIBO stems from a physical problem with their intestine. A surgeon might, for example, be able to eliminate a blind loop where food is getting stuck.

In addition to other treatments, your doctor might recommend changing your diet to help keep SIBO under control.

Diet plans that might help include:

Elimination diets: If you think one or more foods make your symptoms worse, you can try cutting that food from your diet for a short time and then adding it back to see if it makes a difference. For SIBO, doctors sometimes recommend cutting way back on all carbohydrates for a short time. Such a restrictive diet won't be safe for everyone and isn't intended as a long-term solution, so you should always talk to your doctor before trying it.

Elemental diet: This is a more extreme temporary diet in which you get only a liquid formula in which nutrients are already broken down or predigested. This is a way to give your digestive system a rest and is only prescribed for people with severe digestive problems. The diet is not safe for people with diabetes or other blood sugar problems because it may cause spikes in blood sugar.

Low-FODMAP diet: In this diet, you start by cutting out a long list of foods called FODMAPs—fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These are carbohydrate foods that feed the bacteria in your gut and are hard to digest. The list includes many healthy fruits, vegetables, and grains, ranging from apples to onions to wheat, so doctors usually suggest adding foods back one at a time to find which ones you can eat without triggering symptoms. You should work with a health care professional trained in nutrition to make sure you meet all your nutritional needs at every phase of this diet.

Other changes that might help include:

  • Avoiding fiber supplements
  • Avoiding liquid medications (such as cough syrup) that use sugar alcohols for flavor

Without treatment, SIBO can lead to complications including:

Problems absorbing nutrients: You might not absorb enough of the fats, proteins, and carbohydrates from your food. This can lead to to malnutrition and unintended weight loss.

Vitamin shortages: Poor fat absorption can lead to shortages in vitamins A, D, E, and K. One of the most serious complications can be low levels of vitamin B12, which can hurt your nervous system, leading to weakness, fatigue, tingling, numbness in your hands and feet, and, in severe cases, mental confusion. You might not be able to reverse all the damage to your nerves.

Weak bones (osteoporosis): Poor absorption of calcium may mean that not enough of the mineral gets to your bones.

Kidney stones: Low calcium also can lead painful stones to form in your kidneys.

Dehydration: Poor fluid absorption and diarrhea can mean than you lose more fluid than you take in, leading to dehydration, with symptoms like dry mouth and thirst.

Even after you get a diagnosis and treatment with antibiotics, diets, or other measures, your SIBO symptoms might come back.

Getting SIBO under control can mean trying more than one thing. Some people might benefit from:

Adjusting medicines for other conditions. For example, if you are taking narcotics or acid-reducing drugs, you might work with your doctor to cut back.

Physical therapy. Some people get a special type of massage from a physical therapist to break up scar tissue in their gut.

Probiotics. These are live organisms that can help balance gut bacteria. You can get probiotics in fermented foods like yogurt (look for “live, active cultures” on the label), kefir (a yogurt-based drink), and kimchi (a traditional Korean relish). If you're thinking about taking probiotic supplements, talk with your doctor first. In some studies, probiotics have made SIBO symptoms worse.

SIBO is a digestive health problem that shares many symptoms with other common problems, including IBS. It can have many different causes. Sorting out what's causing your problems can lead to effective treatment, so it's important to talk with your doctor about your symptoms.