How Do I Know If I Have SIBO?

SIBO has become one of the most talked-about gut health conditions online. One side says: “Your bloating is probably SIBO.” The other side says: “SIBO is overdiagnosed and breath tests are unreliable.” The truth sits in the middle. SIBO is real, SIBO can be miserable, and SIBO can cause bloating, gas, pain, diarrhoea, constipation, nausea, nutrient issues and food intolerance. But not every bloated stomach is SIBO — and not every case is solved by antibiotics, antimicrobials or another extreme restriction diet.

What Is SIBO and What Causes It?

SIBO stands for small intestinal bacterial overgrowth. The American College of Gastroenterology defines SIBO as excessive bacteria in the small bowel associated with GI symptoms, explaining that these bacteria ferment carbohydrates and produce gas that may contribute to bloating and other symptoms. Your large intestine is designed to house a dense microbial community. Your small intestine is different — it should contain far fewer bacteria because its job is mainly digestion and absorption. When too much fermentation happens there, the result can feel like your gut is inflating from the inside. That is why many people describe SIBO bloating as: “I wake up flat, but by the evening I look pregnant.” That does not diagnose SIBO — but it is a classic clue.

What Are the Most Common SIBO Symptoms?

Symptom Category	Common Signs	SIBO-Specific Pattern
Bloating & gas	Bloating, excessive gas, abdominal pressure, feeling full quickly	Worsens through the day; worse after carbohydrates and fermentable foods
Bowel changes	Diarrhoea, constipation, alternating patterns, urgency, loose stools	Hydrogen-dominant: often diarrhoea; methane-dominant: often constipation
Digestive discomfort	Abdominal pain or cramping, nausea, reflux, feeling full quickly	Often worse 1–2 hours after eating fermentable carbohydrates
Systemic symptoms	Fatigue, brain fog, food reactions, low B12 or iron in some cases	Nutrient issues suggest longer-standing malabsorption; needs medical investigation
Supplement reactions	Probiotics or fermented foods worsen symptoms	Strong SIBO-pattern clue — adding bacteria to an already over-fermenting system

Why Is SIBO So Often Confused With IBS?

SIBO symptoms can overlap heavily with IBS, coeliac disease, inflammatory bowel disease, food intolerances, bile acid diarrhoea, pancreatic insufficiency, gallbladder issues, endometriosis, thyroid problems, medication side effects, stress-driven gut dysfunction, high-FODMAP sensitivity, constipation, pelvic floor dysfunction, gut infection or histamine intolerance. This is why SIBO should not become the new “everything diagnosis.” Sometimes SIBO is the answer. Sometimes it is one piece of the answer. Sometimes it is the wrong direction entirely. The better question is not “do I have SIBO symptoms?” — it is: “do my symptoms follow a SIBO-like pattern, and have other causes been considered?” For more on how IBS and gut pain overlap, read Why Does My Stomach Hurt All the Time?

Why Does SIBO Keep Coming Back After Treatment?

This is the part many people miss. SIBO is often not the root problem — it is the result of something else. The ACG guideline notes that SIBO is, in many cases, related to an underlying issue that allows bacteria to accumulate in the small bowel, especially problems that lead to stasis, including mechanical or motility disorders. Your small intestine has a cleaning wave — the migrating motor complex — that between meals helps move bacteria and leftover material down into the large intestine. If that movement is sluggish, bacteria can hang around where they should not. Possible contributors include food poisoning history, post-infectious IBS, constipation, low thyroid function, diabetes-related motility problems, abdominal surgery, adhesions, long-term gut inflammation, certain medications, chronic stress, irregular eating patterns, frequent grazing, low stomach acid and structural issues. This is why repeatedly “killing bacteria” without asking why they are overgrowing can lead to relapse. If the drain is blocked, mopping the floor is not enough.

What Do Real SIBO Patterns Look Like?

Case Study 1: “Healthy Eating Made Me Worse”

Someone tries to eat healthier and adds lentils, chickpeas, onions, garlic, apples, avocado, protein bars, inulin, fibre powders, kombucha, fermented foods and high-prebiotic snacks. Then their bloating explodes. They feel confused because everything they added was supposed to be “good for gut health.” But if the small intestine is already over-fermenting, throwing more fermentable fuel into the system can make things worse. That does not mean fibre is bad — it means timing and tolerance matter. The answer is not “never eat fibre again.” The answer is: reduce the noise, identify tolerance, rebuild slowly, and find out why fermentation is happening in the wrong place. SIBO is not just a food problem. It is often a motility problem.

Case Study 2: “Antibiotics Helped, Then It Came Back”

Someone gets diagnosed with SIBO, takes antibiotics or herbal antimicrobials, and for two or three weeks feels better — less bloating, less gas, better appetite, more energy. Then slowly, symptoms return. They think: “The treatment failed.” But another possibility is that the treatment reduced bacteria, but the underlying environment did not change. The motility issue remained, constipation remained, stress remained, meal timing remained chaotic, sleep remained poor, the gut lining remained irritated. This is where SIBO needs a system, not just a short-term attack plan. Understand the system that allowed the problem to develop. That is the difference between symptom management and root-cause thinking.

Case Study 3: “It’s Actually Constipation”

A person feels bloated, gassy, heavy and inflamed. They test for SIBO and may even get a positive methane result. But beneath it all, their bowel movements are slow and incomplete — they go daily, but never fully empty. Constipation itself can create fermentation, gas retention and bacterial imbalance. In methane-dominant patterns, constipation is common, but the solution still has to address motility and bowel clearance, not just bacteria. A person may need to look at hydration, electrolytes, meal rhythm, soluble fibre tolerance, magnesium suitability, movement, pelvic floor function, thyroid status, stress biology and medication side effects. The better question is not “do I go every day?” It is: “do I empty fully and comfortably?”

How Is SIBO Tested and How Reliable Are Breath Tests?

The most common non-invasive test is a hydrogen and methane breath test. Humans do not directly produce hydrogen or methane — these gases are produced when microbes ferment undigested carbohydrates, and some of that gas enters the blood and is breathed out through the lungs. The British Society of Gastroenterology explains that hydrogen and methane breath testing is used to assess SIBO and carbohydrate malabsorption, while also noting controversy and inconsistent interpretation between centres. But breath testing is imperfect: it can produce false positives, false negatives, different clinics use different methods, preparation affects results, and fast transit or constipation can complicate the picture. Guts UK warns that breath testing has produced false positives in healthy people and that a positive test does not reliably predict whether treatment will work. A test is data. It is not the whole truth. Your symptom pattern, medical history, risk factors and clinician’s interpretation all matter.

What Should You Do If You Suspect SIBO?

Stop stacking random gut supplements. Probiotics, antimicrobials, digestive enzymes, fibre powders, laxatives, binders and fermented foods all change the picture. If you do everything at once, you learn nothing.

Track your pattern for two weeks. Record meals, bloating, pain, gas, stool frequency and form, urgency, constipation, sleep, stress, menstrual cycle if relevant, supplements, medication, trigger foods and time of day symptoms worsen. This gives you data, not drama.

Speak to a professional before aggressive treatment. SIBO treatment often involves antibiotics or antimicrobial protocols. These should not be approached casually. A professional can help decide whether testing is appropriate, whether other conditions need ruling out, and whether your pattern fits SIBO or something else.

Look for the root pattern. Is this diarrhoea-dominant, constipation-dominant, post-infectious, stress-driven, motility-related, food-triggered, medication-related, linked to surgery or structural issues, or associated with nutrient deficiencies? The answer shapes the plan.

Rebuild, do not just restrict. Low-FODMAP or low-fermentation diets may reduce symptoms short-term, but staying overly restricted can reduce food diversity and worsen fear around eating. The long-term aim is better motility, better bowel regularity, better food tolerance, better meal rhythm, better stress regulation and better microbiome resilience. For more on rebuilding the gut environment, read Can You Heal Your Gut Microbiome Naturally?

Frequently Asked Questions

Can SIBO go away on its own?
In mild cases, particularly where the trigger was temporary (such as a short course of antibiotics or a single gut infection), symptoms may improve with dietary support and time. However, if an underlying motility issue, structural problem or chronic condition is driving bacterial overgrowth, SIBO is unlikely to resolve without addressing the root cause. Persistent or worsening symptoms should be assessed by a healthcare professional.

What foods should I avoid if I suspect SIBO?
A low-FODMAP or low-fermentation approach is often used short-term to reduce symptoms — this typically means reducing onions, garlic, wheat, apples, pears, beans, lentils, lactose and sugar alcohols. However, this is not a long-term solution. The goal is to reduce fermentable load temporarily while addressing the underlying cause, then gradually rebuild food tolerance. Indefinite restriction without a reintroduction plan can worsen gut resilience over time.

Is SIBO the same as IBS?
No — but they can overlap significantly. IBS is a disorder of gut-brain interaction characterised by abdominal pain and changes in bowel habits. SIBO is a specific pattern of bacterial overgrowth in the small intestine. Some people with IBS may have SIBO as a contributing factor, but most IBS is not caused by SIBO. UK IBS guidelines advise against routine breath testing for IBS because there is limited proof that breath testing effectively diagnoses SIBO in people with IBS.

Can probiotics make SIBO worse?
For some people, yes. If the small intestine is already over-fermenting, adding more bacteria — even beneficial strains — can increase gas, bloating and discomfort. This is one of the more distinctive SIBO-pattern clues: worsening symptoms on probiotics or fermented foods. If this is your experience, it is worth discussing with a professional rather than pushing through.

How long does SIBO treatment take?
Antibiotic or antimicrobial treatment for SIBO typically lasts two to four weeks. However, symptom improvement and full recovery depend heavily on addressing the underlying cause — particularly motility, bowel rhythm, diet and stress. Without addressing root factors, relapse rates are high. A structured rebuilding phase after treatment is as important as the treatment itself.