SIBO: What It Is, Symptoms, Causes, and When to See a Specialist

If you deal with bloating or gas after meals, you've likely wondered whether a certain food is to blame. Maybe you've even tried cutting out dairy, gluten, or other foods without improvement.

Sometimes, the problem isn't the food itself, it may be small intestinal bacterial overgrowth (SIBO), a condition in which bacteria build up in the small intestine. Because the symptoms are similar to irritable bowel syndrome (IBS) and other digestive conditions, SIBO isn't always easy to recognize.

This article explains what SIBO is, its symptoms, what causes it, how it's diagnosed, and the treatment options available.

What Is SIBO (Small Intestinal Bacterial Overgrowth)?

Most of your gut bacteria live in the large intestine. The small intestine also contains bacteria, but in much lower amounts.

SIBO develops when bacteria build up in the small intestine and cause overgrowth.

The bacteria ferment, or break down, carbohydrates before they can be properly digested, producing excess gas, like hydrogen, methane, and hydrogen sulfide, that can interfere with normal digestion and cause symptoms like bloating.

Common Symptoms of SIBO

Bloating, gas, abdominal pain, nausea, and changes in bowel habits are common symptoms of SIBO. However, these symptoms are also common in IBS and other digestive conditions, making it difficult to know whether SIBO is the underlying cause.

Bloating and Gas

Bloating is generally the most bothersome symptom of SIBO. The abdomen may feel swollen, tight, or uncomfortably full, and excess gas can cause belching or flatulence (passing gas).

Bloating tends to worsen after meals and be more noticeable as the day goes on, some people even describe feeling several months pregnant.

Changes in Bowel Habits

SIBO can cause diarrhea, constipation, or a mix of both. Which one you experience may depend on the type of gas produced by bacteria in the small intestine. Methane is commonly associated with constipation, while hydrogen sulfide is more often linked to diarrhea.

Abdominal Pain and Discomfort

Abdominal pain may feel like cramping, aching, or pressure, especially after eating, even if it's a smaller meal. For some people, it happens only once in a while. For others, it's frequent enough to make everyday activities uncomfortable.

Having a bowel movement may offer some relief, but it's usually temporary.

Nutrition-Related Symptoms

When SIBO makes it harder for your body to absorb nutrients from food, some people experience unintentional weight loss, low energy, and steatorrhea, a condition that causes pale, oily, foul-smelling stools that float.

SIBO can also make it harder to absorb nutrients like iron, vitamin B12, and vitamins A, D, E, and K, which may contribute to vitamin and mineral deficiencies.

What Causes SIBO?

Bacteria don't typically have the chance to build up in the small intestine because your body is regularly moving food through the digestive tract. Muscle contractions push food along, while stomach acid, bile, digestive enzymes, and the immune system help limit bacterial growth.

SIBO develops when one or more of these systems isn't working as it should. Food stays in the small intestine longer than it should, giving bacteria more time to multiply.

Most of the time, SIBO doesn't happen on its own. It's usually a sign that something else, like slowed movement through the small intestine or changes to the digestive tract, is making it easier for bacteria to build up.

Slowed Intestinal Movement

According to a 2025 review in Current Opinion in Gastroenterology, conditions that slow the normal movement of the small intestine can increase the risk of SIBO, because when food and bacteria are in the small intestine longer than normal, bacteria have more time to grow.

This can happen with conditions such as diabetes, Parkinson's disease and other neurological disorders, hypothyroidism, scleroderma, and IBS.

Structural Changes to the Digestive Tract

Changes to the digestive tract can also make it easier for bacteria to build up.

This may happen because of scar tissue (adhesions), narrowed areas of the intestine (strictures), bowel obstructions, intestinal diverticula, fistulas, or previous abdominal or bariatric surgeries.

Other Factors That Increase Risk

Several other health conditions have also been linked to SIBO, including Crohn's disease, celiac disease, chronic pancreatitis, cirrhosis, and immune deficiencies.

Certain medications may also increase the risk of SIBO, including long-term or repeated antibiotic use and proton pump inhibitors (PPIs).

Some research suggests SIBO also becomes more common as people get older, and women may be slightly more likely to develop it.

How SIBO Is Diagnosed

SIBO can be difficult to diagnose because its symptoms overlap with many other digestive conditions. But if your symptoms and health history suggest SIBO, your doctor may recommend testing for bacterial overgrowth.

Testing

According to a 2023 review, breath testing is the most common test for SIBO because it's noninvasive and widely available.

During the test, you'll drink a sugar solution, usually glucose or lactulose, and provide breath samples over the next two to three hours. If excess bacteria are present in the small intestine, they'll ferment the sugar and produce hydrogen, methane, or hydrogen sulfide gas that can be measured in your breath.

In some cases, your healthcare provider may collect a small sample of fluid from your small intestine during an upper endoscopy. Because this test is more invasive and expensive than a breath test, it's used much less often.

Other Considerations

Your doctor will consider your symptoms alongside your medical history. You may also need additional testing to look for the underlying cause of SIBO or rule out other digestive conditions with similar symptoms, such as celiac disease, inflammatory bowel disease, or lactose intolerance.

When to See a Specialist

See your healthcare provider if you've had persistent bloating, abdominal pain, changes in bowel habits, or unexplained weight loss. You should also follow up if your symptoms don't improve with treatment or return after improving.

Finding the cause of your symptoms can help you get the right treatment and lower the chance that SIBO will come back.

Treatment Options for SIBO

Treatment for SIBO has two goals: reducing the bacterial overgrowth and targeting the root cause. Both are important because SIBO often returns if the factors that allowed it to develop, such as slowed intestinal movement or structural changes in the digestive tract, aren't managed.

Your treatment plan will consider your symptoms, test results, medical history, and health comorbidities.

Medical Treatment

Antibiotics are the primary treatment for SIBO because they help reduce bacterial overgrowth in the small intestine. The type of antibiotic depends on your symptoms and breath test results. Some people improve after a single course of treatment, while others may need additional treatment if symptoms persist or return.

Just as importantly, your healthcare provider will work to identify and treat the underlying cause whenever possible. Depending on the situation, this may involve managing an underlying digestive or medical condition, reviewing medications that may contribute to SIBO, improving intestinal motility, or correcting nutrient deficiencies.

Because SIBO can recur, follow-up care is often an important part of long-term management.

Dietary Changes and Nutrition Support

While diet can't cure SIBO, it can help manage symptoms.

Instead of eating frequently throughout the day, some providers recommend leaving 3 to 5 hours between meals. This gives the migrating motor complex (MMC), a series of muscle contractions that moves food and bacteria through the small intestine, a chance to do its job.

Your doctor may also recommend a temporary low-FODMAP diet. This eating plan limits certain carbs that are easily fermented by gut bacteria and may help reduce bloating, gas, and abdominal discomfort.

An elemental diet may be recommended if other treatments haven't helped. Because it only includes specially formulated liquid nutrition and is very restrictive, it should be used under medical supervision.

Working with a Registered Dietitian

There's no single eating plan that works for everyone with SIBO. A gut health nutritionist can help you identify foods or eating habits that may be triggering your symptoms while making sure you're still getting the calories and nutrients your body needs.

If you're prescribed an elimination diet, a dietitian can help you plan balanced meals without cutting out more foods than necessary. As your symptoms improve, they'll guide you through reintroducing foods one at a time to identify what you tolerate. The goal is to build the most varied diet possible, not stay on a restrictive eating plan long-term.

Many insurance plans cover nutrition counseling for digestive conditions. Check your benefits to see whether visits with a registered dietitian are covered.

Living with SIBO: What to Expect

SIBO treatment doesn't always end after a single course of therapy. For many people, managing SIBO is an ongoing process because symptoms can return, especially if the underlying cause, such as slowed gut motility, structural changes in the digestive tract, or another medical condition, isn't addressed.

Understanding why SIBO developed in the first place can help reduce the risk of recurrence and guide long-term management.

Preventing SIBO from Coming Back

The best way to prevent SIBO from coming back is to treat the underlying cause. Depending on the cause, this may include improving how food moves through the small intestine, treating an underlying digestive condition, or addressing structural problems that allow bacteria to build up.

Keep in touch with your doctor, especially if your symptoms return or change over time. Regular follow-up can help determine whether your treatment plan needs to be adjusted.

Some people need additional treatment if SIBO comes back. This doesn't mean treatment has failed. It may simply reflect an underlying condition that continues to increase the risk of bacterial overgrowth.

With the right treatment, many people can manage their symptoms, reduce recurrences, and improve their quality of life.

When to Seek Additional Support

Consider seeking support if:

• Your symptoms return after treatment
• You develop new symptoms or your bloating, abdominal pain, diarrhea, or constipation become more frequent or severe
• You're unintentionally losing weight
• You're having difficulty eating enough or are concerned about nutrient deficiencies
• Your symptoms aren't improving despite treatment

Persistent digestive symptoms can be frustrating, but you don't have to live with them. Your healthcare provider can determine whether additional evaluation or treatment is needed and connect you with specialized nutrition or digestive health support when appropriate.

Getting the right support can help you better manage your symptoms and improve your quality of life.

Getting Started with Professional Support

SIBO is a treatable condition, but getting the right diagnosis is important because its symptoms overlap with many other digestive disorders. Rather than experimenting with trial and error or cutting out more and more foods on your own, work with a healthcare provider to identify the underlying cause and develop a treatment plan that's right for you.

Working with a gut health nutritionist can also help you navigate SIBO treatment. They can help you meet your nutrition needs, identify potential food triggers, and build an eating pattern that supports your digestive health during and after treatment.

If you're managing SIBO, Top Nutrition Coaching can match you with a registered dietitian to help build an eating pattern that fits your treatment plan. See if your insurance covers a registered dietitian before your first visit.

Frequently Asked Questions

What is SIBO and how do I know if I have it?

SIBO is a condition when too many bacteria grow in the small intestine. It commonly causes bloating, gas, abdominal pain, diarrhea, constipation, or a combination of these symptoms. Since many digestive conditions can look similar, your healthcare provider may recommend a hydrogen and methane breath test if SIBO is suspected.

What are the most common symptoms of SIBO?

SIBO commonly causes bloating, gas, abdominal pain, diarrhea, constipation, and a feeling of fullness after eating. It can also interfere with nutrient absorption, leading to vitamin deficiencies or unintentional weight loss.

Are breath tests accurate for diagnosing SIBO?

Breath tests are the most widely used noninvasive test for SIBO, but no test is 100 percent accurate. They can provide helpful information, but results should always be interpreted alongside your symptoms and medical history since false positives and false negatives are possible.

What causes SIBO and who is at risk for developing it?

SIBO develops when bacteria that are normally kept at low levels in the small intestine grow in excess. Risk is higher in people with conditions that slow digestion or alter the digestive tract, including diabetes, celiac disease, inflammatory bowel disease (IBD), or prior gastrointestinal surgery. Long-term use of proton pump inhibitors and opioids may also increase the risk.

Can SIBO be cured permanently or does it keep coming back?

SIBO can be treated successfully, but it often comes back, especially if the underlying cause isn't addressed. Conditions that affect gut motility, structural changes to the digestive tract, and some medications can increase the risk of recurrence. Working with your healthcare provider to identify and manage these underlying factors offers the best chance of long-term symptom relief.

How long does SIBO treatment take and what should I expect?

Treatment for SIBO typically begins with a 10- to 14-day course of antibiotics, although the exact treatment plan depends on your symptoms and underlying cause. You may notice improvement within a few weeks, but some require additional treatment if symptoms persist or return. Because SIBO often develops as a result of another digestive or medical condition, long-term success depends on treating both the bacterial overgrowth and the underlying cause.

Which diet works best for SIBO: low FODMAP, elemental, or SCD?

There isn't one diet that's considered best for SIBO. An elemental diet may be recommended in certain cases when other treatments haven't worked, but it should only be used under medical supervision. A low FODMAP diet has the strongest evidence for reducing symptoms like bloating and gas, although it hasn't been shown to eliminate SIBO and is intended as a short-term strategy. The Specific Carbohydrate Diet (SCD) may also be prescribed, but there is currently limited evidence to support its use specifically for SIBO.

Can SIBO cause fatigue, brain fog, and nutrient deficiencies?

Yes, SIBO can contribute to nutrient deficiencies, especially vitamin B12, iron, and fat-soluble vitamins, and may contribute to symptoms like fatigue. Some people with SIBO also report brain fog, but the evidence linking SIBO cognitive symptoms is still limited, and many other conditions can cause similar symptoms.