Bloating, Gas, and Pain: Could SIBO Be Masquerading as IBS?

by Kat Pachas BSN, RN

Bloating, that uncomfortable feeling when your belly feels tight and full, is something many people deal with now and then. It often happens after eating a big meal full of carbohydrates, like a large plate of your favorite spaghetti. But bloating can also be caused by health conditions. Many people know about irritable bowel syndrome (IBS), but small intestinal bacterial overgrowth (SIBO) could also be behind your painful bloating, even though many people have not heard of it before.

IBS is a common digestive problem in the United States, affecting about 10% to 15% of adults. It causes symptoms in the stomach and intestines. People with IBS often have bloating, stomach pain, gas, diarrhea, constipation, or sometimes both. Many patients get blood tests or procedures like an endoscopy, where a small camera looks at the digestive tract, and are told their results look normal. When this happens, doctors may call it a functional disorder, meaning the gut is not working properly. Treatment usually focuses on managing IBS symptoms day to day.

But what if IBS is only part of the story? SIBO could also play a role in your digestive problems. Many people have not heard of SIBO, but research shows that up to 60–70% of IBS cases may be linked to it. This does not mean all IBS is caused by SIBO, but it suggests that some cases of IBS may have a treatable cause.

What Is SIBO?

SIBO can develop when bacteria from the large intestine move into the small intestine and start to multiply. The small intestine is not meant to have a lot of bacteria. When there are too many, they can interfere with digestion. These bacteria break down carbohydrates from your food and produce gases like methane, hydrogen, or hydrogen sulfide, which leads to even more gas. This extra gas stretches the small intestine, causing pain, bloating, and other symptoms [3]. Many people with SIBO say they look "six months pregnant" by the end of the day.

          Other symptoms include:

• Bloating

• Abdominal pain

• Abdominal distension

• Diarrhea.

• Constipation

• Nausea

• Indigestion

• Gas

• Unintentional weight loss

• Fatigue

• Stomach discomfort

• Visible swelling

• Symptoms worsening after meals

• Loss of appetite

SIBO can also cause problems with absorbing fat, which can make your stool float, smell bad, or look oily. Over time, too many bacteria in the small intestine can interfere with how your body digests nutrients, leading to vitamin and mineral deficiencies [3].

Why SIBO Happens

SIBO can develop for several reasons, and it is more common in people whose gut moves more slowly. The small intestine has a cleaning system called the migrating motor complex, or MMC. Between meals, your gut sends waves every 90 to 120 minutes to move leftover food and bacteria into the large intestine. You can think of this as your gut’s dishwasher cycle. If this process slows down because of IBS, infections, diabetes, connective tissue problems, past abdominal surgery, or certain medications like proton pump inhibitors for acid reflux, food and bacteria can stay in your gut longer. A bout of food poisoning or viral illness can also slow down the MMC. These changes can create conditions that may lead to SIBO [3].

IBS and SIBO: Understanding the Connection

IBS happens when the gut and brain do not communicate well, so signals between the digestive and nervous systems get mixed up [4]. This makes the gut more sensitive, and normal digestion can feel painful. This extra sensitivity can slow down how the gut moves, which lets bacteria build up. Studies show that people with IBS are much more likely to test positive for SIBO than those without digestive problems. However, having IBS does not always mean you have SIBO. If your symptoms keep coming back or are getting worse, it is worth looking into further.

Diagnosing SIBO

Doctors usually diagnose SIBO with a breath test. For the test, you will fast for 12 hours beforehand. On the day of the test, you drink a sugar solution with lactulose or glucose and blow into a plastic bag with a tube attached for 10 seconds at intervals of 15-30 minutes over 2 to 3 hours. When bacteria in the small intestine break down the sugar, they produce hydrogen or methane, which is absorbed and then released in your breath. The sealed bags are sent to a lab to measure the gas levels. If these levels are higher than normal, you may be diagnosed with SIBO. A rise of more than 20 ppm (parts per million) in hydrogen within 90 minutes, or a methane level over 10 ppm, is considered a positive result [7]. Breath tests are easy and non-invasive, but they are not perfect. Sometimes they give false-positive or false-negative results, and can be affected by how quickly things move through your gut. Even with these limits, breath testing is still the most common noninvasive way to diagnose SIBO.[6]

Treatment Options for Sibo

Treating SIBO focuses on three main goals: lowering the extra bacteria, easing symptoms, and fixing the root cause so the problem does not come back.[6,7]

1. Antibiotics

The most common way to treat SIBO is with a short course of antibiotics to lower the number of bacteria in the small intestine. Rifaxin is often used because it mostly stays in the digestive tract instead of spreading through the whole body. This helps it target the bacteria in the gut and usually causes fewer side effects. Antibiotic treatment usually lasts 10 to 14 days, but some people need more than one round if symptoms come back.

2. Dietary Changes

Diet can help manage symptoms and keep bacteria from growing too much again. While foods do not cause SIBO, certain foods like sugars, sweeteners, starches, fruits, dairy products, and grains can encourage the wrong bacteria to grow in your small intestine and trigger more SIBO symptoms. You can help reduce the overgrowth by avoiding the foods that bacteria like most.

Some doctors recommend a low-FODMAP diet for SIBO, which limits certain carbohydrates that bacteria easily ferment, causing gas, bloating, and discomfort. Another option is the elemental diet, a liquid nutrition plan that gives nutrients in a form your body can absorb quickly in the upper digestive tract. Because these nutrients are absorbed fast, bacteria farther down in the intestine have less to feed on. Doctors often suggest these dietary changes along with antibiotics.

3. Treating the Underlying Cause

SIBO often develops when something disrupts normal digestion or the movement of the intestines. If the main problem is not fixed, the bacterial overgrowth can return.

Common contributing factors include:

• Slow intestinal motility

• Structural problems in the digestive tract

• Certain medications

• Conditions affecting digestion

  
  

For example, people with IBS, diabetes, or celiac disease have a higher risk of getting SIBO. Managing these conditions can help lower the chance of SIBO returning. Some people may also benefit from medications that help the gut move food and bacteria through the digestive tract more efficiently. These are sometimes called prokinetic agents.

4. Nutritional Support

Because SIBO can interfere with nutrient absorption, some people develop deficiencies over time. Correcting these deficiencies can help increase your energy and improve your overall health. Doctors may recommend supplements such as:

• Vitamin B12

• Iron

• Fat-soluble vitamins (A, D, E, and K)

When to Seek Help

See a gastroenterologist if you experience:

• Unexplained weight loss

• Blood in stool

• Persistent vomiting

• Anemia

• Symptoms that wake you from sleep

• Rapidly worsening symptoms

  
  

The Bottom Line

If you have been told you have IBS, learning about SIBO can give you another option for diagnosing and treating your digestive problems. If you feel bloated after every meal, if your symptoms started after food poisoning, or if standard IBS treatments have not worked, it may be worth talking to your healthcare provider. SIBO can be treated, but it often takes several steps. Digestive symptoms can affect your nutrition, mental health, daily life, and overall well-being. While IBS is a common diagnosis, SIBO may be an important factor to consider. Discussing testing for SIBO with your healthcare provider may help you get more targeted treatment and help improve your quality of life.

References

1. Cleveland Clinic. (n.d.). Irritable bowel syndrome (IBS). Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/4342‑irritable‑bowel‑syndrome‑ibs

2. Šuran, J., Pavlović, N., Božić, J., Kumrić, M., Vukojević, K., Filipović, N., & Radić, B. (2026). IBS and SIBO: Gut Microbiota, Pathophysiology, and Non-Pharmacological Interventions. Antibiotics, 15(3), 251. https://doi.org/10.3390/antibiotics15030251

3. Dukowicz, A. C., Lacy, B. E., & Levine, G. M. (2007). Small intestinal bacterial overgrowth: a comprehensive review. Gastroenterology & hepatology, 3(2), 112–122.

4. Raskov, H., Burcharth, J., Pommergaard, H. C., & Rosenberg, J. (2016). Irritable bowel syndrome, the microbiota and the gut-brain axis. Gut microbes, 7(5), 365–383. https://doi.org/10.1080/19490976.2016.1218585

5. Spiegel, B. M., Chey, W. D., & Chang, L. (2008). Bacterial overgrowth and irritable bowel syndrome: unifying hypothesis or a spurious consequence of proton pump inhibitors?. The American journal of gastroenterology, 103(12), 2972–2976. https://doi.org/10.1111/j.1572-0241.2008.01992.x

6. Skrzydło-Radomańska, B., & Cukrowska, B. (2022). How to Recognize and Treat Small Intestinal Bacterial Overgrowth?. Journal of clinical medicine, 11(20), 6017. https://doi.org/10.3390/jcm11206017

7. Sorathia, S. J., Chippa, V., & Rivas, J. M. (2023). Small intestinal bacterial overgrowth. In StatPearls. StatPearls Publishing.

Assessed and Endorsed by the MedReport Medical Review Board