SIBO can cause a wide range of digestive and non-digestive symptoms, including bloating, abdominal discomfort, changes in bowel habits, nausea, fatigue and brain fog. Because these symptoms overlap with conditions such as IBS and food intolerances, testing is often needed to understand what is really driving them.
A structured, evidence-informed approach that combines appropriate SIBO breath tests, personalised nutrition and lifestyle support can help reduce symptoms and provide clearer direction, rather than relying on guesswork or short-term fixes.
If you’re searching for common symptoms of SIBO, there’s a good chance you’re dealing with digestive symptoms that don’t quite add up. You may notice bloating that seems out of proportion to what you eat, discomfort after meals, or changes in bowel habits that come and go. Perhaps you have tried adjusting your diet or using over the counter products, but symptoms keep returning or shifting rather than fully settling.
SIBO, short for small intestinal bacterial overgrowth, is often considered when digestive symptoms feel persistent, confusing or overlap with conditions such as IBS. It can be difficult to tell what is really driving how you feel, especially as many gut conditions share similar symptoms – take a look at our article on SIBO vs Candida, for example. This uncertainty is often what leads people to look for clearer explanations and more structured support.
In this article, we’ll walk through the most common symptoms associated with SIBO, explain what may be happening in the body, and look at why testing can be an important step. We will also cover when symptoms may point to something other than SIBO, how symptoms can be supported, and how a functional medicine approach at IBS Clinics may help guide recovery in a safe, personalised way.
What Is SIBO? A Brief Overview
SIBO stands for small intestinal bacterial overgrowth. It describes a situation where bacteria that normally live in the large intestine begin to build up in the small intestine, where they do not belong in large numbers. The small intestine is designed for digestion and nutrient absorption, not fermentation, so this imbalance can interfere with how food is broken down and absorbed.
When these bacteria come into contact with carbohydrates and fibres, they can produce excess gas and other by-products. This can lead to symptoms such as bloating, abdominal discomfort, changes in bowel habits and feelings of fullness soon after eating. Over time, SIBO may also contribute to nutrient deficiencies and symptoms beyond the gut, which is why it is often considered when digestive issues feel persistent or difficult to explain.
Common Symptoms of SIBO
SIBO can present in a variety of ways, which is one reason it is often missed or confused with other gut conditions. Symptoms may develop gradually or fluctuate over time, and many people notice they’re worse after eating (1).
One of the most common symptoms is bloating, often described as feeling distended or uncomfortably full, sometimes even after small meals. This is frequently accompanied by excess gas, burping or abdominal pressure. Abdominal discomfort or pain is also common and may feel crampy, achy or linked to bowel movements (1,2).
Changes in bowel habits are another key feature. Some people experience diarrhoea, others constipation, and some alternate between the two. Nausea, a sense of early fullness, or feeling unwell after meals can also occur, particularly when foods that ferment easily are eaten (2).
Beyond the gut, some people notice symptoms such as fatigue, weakness or difficulty concentrating, which may relate to poor nutrient absorption or the overall strain that ongoing digestive symptoms place on the body. Because these symptoms overlap with many other conditions, SIBO is rarely identified based on symptoms alone, which is why further assessment and testing are often important (1).
What Is Happening in Your Body with SIBO?
In a healthy digestive system, the small intestine contains relatively low levels of bacteria. Its job is to break down food and absorb nutrients efficiently. With SIBO, bacteria that are normally found further down in the digestive tract begin to accumulate in the small intestine, disrupting this process (2).
As food passes through the small intestine, these bacteria ferment carbohydrates before they should. This fermentation produces gases such as hydrogen or methane, which can slow or speed up gut movement and contribute to bloating, pain, diarrhoea or constipation. The type of gas produced can also influence the pattern of symptoms someone experiences (1,2).
Over time, this bacterial activity can interfere with digestion and nutrient absorption. Bacteria may compete with the body for nutrients such as vitamin B12, iron and fat-soluble vitamins, which can contribute to symptoms beyond the gut, including fatigue, weakness or brain fog. Ongoing irritation of the gut lining may also increase sensitivity, making the digestive system react more strongly to foods that were previously tolerated (2).
From a functional medicine perspective, SIBO is often viewed as a sign of microbial imbalance rather than an isolated condition. Factors such as reduced gut motility, stress, previous infections, medication use or structural issues in the gut can all influence why bacteria are able to build up in the small intestine in the first place. Understanding these contributing factors is an important part of supporting recovery and reducing the risk of symptoms returning (3).
Conditions with Overlapping Symptoms
One of the challenges with SIBO is that its symptoms overlap with several other digestive conditions. Bloating, abdominal discomfort, changes in bowel habits and nausea are not unique to SIBO, which is why it can be difficult to identify based on symptoms alone (1,2).
IBS is the most common condition SIBO is confused with. Many people with IBS experience similar patterns of bloating, pain, diarrhoea or constipation, and some may actually have both conditions at the same time. Because the symptoms can look almost identical, it is not possible to tell from how you feel alone whether SIBO is contributing (1).
Food intolerances can also present in a similar way. Symptoms such as bloating, gas or loose stools after eating may be linked to difficulty digesting certain foods, rather than bacterial overgrowth itself. Without proper assessment, this can lead to repeated food restriction without addressing the underlying issue (1).
Coeliac disease and other gut conditions can also cause digestive symptoms that resemble SIBO, particularly when malabsorption or gut inflammation is involved. This is one of the reasons medical assessment is important before assuming SIBO is the cause of symptoms, especially if symptoms are severe, worsening or accompanied by weight loss or nutrient deficiencies (2).
Because so many gut conditions share similar symptoms, testing and clinical context matter. Understanding whether SIBO is present, or whether symptoms may be better explained by another condition, helps guide safer and more effective next steps.
Why Testing Matters for Suspected SIBO
Because SIBO shares symptoms with many other digestive conditions, symptoms alone are not enough to know what’s really going on. Bloating, pain, diarrhoea or constipation can point in several directions, and assuming SIBO without testing can lead to inappropriate or ineffective strategies (1,2).
Testing helps provide clarity. It allows you and your practitioner to assess whether bacterial overgrowth is likely to be contributing to symptoms, or whether another explanation should be explored instead. This reduces guesswork and helps avoid unnecessary dietary restriction or repeated trial-and-error approaches that may not address the underlying issue (1).
Symptoms That May Suggest Something Other Than SIBO
While SIBO can cause uncomfortable and persistent symptoms, certain signs should always be checked by a GP or specialist, as they may indicate another condition. These include
- unexplained weight loss
- persistent vomiting
- ongoing or severe abdominal pain
- blood in the stool
- anaemia
- or symptoms that worsen rapidly (2).
These features are not typical of uncomplicated SIBO and require medical assessment. Testing for SIBO should always sit alongside appropriate medical evaluation, particularly if symptoms are new, severe or changing in nature.
How SIBO Breath Tests Work
The most common way to investigate SIBO is through a breath test. This involves drinking a sugar solution, usually glucose or lactulose, and then providing breath samples at regular intervals over a few hours. These samples are analysed for gases such as hydrogen and methane, which are produced when bacteria ferment the sugar (1,2).
In a healthy digestive system, most fermentation happens in the large intestine. With SIBO, fermentation occurs earlier, in the small intestine, leading to a rise in these gases sooner than expected. Measuring this pattern helps identify whether bacterial overgrowth may be present and whether hydrogen, methane or a combination of both gases is dominant. This information can then help guide next steps in a more targeted and informed way (1,3).
How SIBO Symptoms May Be Alleviated
Managing SIBO symptoms often involves a combination of dietary strategies, lifestyle adjustments and targeted symptom support, rather than a single solution. Because symptoms can vary widely, what helps one person may not be appropriate for another, which is why a flexible, individualised approach is important (1).
Dietary changes are commonly used to help reduce symptom burden. This may include temporarily adjusting carbohydrate intake or identifying foods that worsen bloating or discomfort. The goal is not long-term restriction, but to reduce fermentation in the short term while other contributing factors are explored (1). Lifestyle factors also matter. Supporting regular meals, adequate sleep, gentle movement and stress management can all influence how the digestive system functions and how strongly symptoms are felt day to day (2).
Symptom support may also include carefully selected supplements or practical strategies aimed at easing bloating, discomfort or bowel irregularity. These are typically used to support comfort and function, not as a cure, and are best reviewed regularly to ensure they remain appropriate as symptoms change (3).
How a Functional Medicine Practitioner Can Support SIBO Recovery
A functional medicine practitioner supports SIBO recovery by looking beyond symptom relief alone and helping to identify why bacterial overgrowth may have developed in the first place. From this perspective, SIBO is often viewed as a sign of microbial imbalance influenced by factors such as gut motility, stress, previous infections, medication use or broader lifestyle patterns (3).
Support is personalised and collaborative. Rather than following a fixed protocol, a practitioner works with you to build a plan that fits your symptoms, history and capacity for change. This may involve guidance around nutrition, lifestyle adjustments, appropriate testing and interpretation, and ongoing review as your body responds over time (3).
Importantly, functional medicine does not position itself as a treatment or cure for SIBO. Instead, it offers a structured way to support recovery, reduce symptom burden and lower the risk of symptoms returning by addressing contributing factors alongside symptom management (3).
The IBS Clinics Approach to SIBO
At IBS Clinics, SIBO is approached as part of a wider picture rather than a standalone diagnosis. Symptoms are explored alongside factors such as digestion, stress, sleep, diet, lifestyle and previous health history, recognising that bacterial overgrowth in the small intestine is often influenced by multiple contributing factors rather than a single cause (3).
Testing plays an important role in this process. Where SIBO is suspected, breath testing is used to help identify whether bacterial overgrowth is likely to be contributing to symptoms and which gases are involved. Results are not viewed in isolation. They are interpreted in the context of symptoms, medical history and day to day patterns, helping to avoid assumptions based on test results alone (1,2).
Nutrition and lifestyle support are then tailored to the individual. Rather than applying a rigid or long-term restrictive diet, guidance focuses on reducing symptom burden, supporting digestion and helping the gut environment recover. Lifestyle factors such as meal timing, stress load, sleep quality and daily routines are also considered, as these can strongly influence gut function and symptom severity (3).
Personalised plans are reviewed and adjusted over time. Support is collaborative and responsive, with follow-up sessions used to interpret test results, refine strategies and respond to changes as symptoms evolve. The aim is not just short-term symptom relief, but a clearer understanding of what may be driving SIBO-related symptoms and how to support more sustainable improvement.
Next Steps
If SIBO is something you’re exploring, the next step is to get clear on whether testing and functional support are appropriate for your symptoms. At IBS Clinics, this usually begins with a free introductory call, where you can talk through your concerns, ask questions and understand how the process works. This call is designed to map out options only and does not include personalised advice.
If you decide to move forward, you may then book a personalised consultation, which allows time to explore your symptoms, history and possible contributing factors in more detail. Where appropriate, SIBO breath tests can be arranged, with results reviewed and explained during a dedicated interpretation session so you understand what they mean and how they inform your next steps.
From there, ongoing support can be tailored around you, combining nutrition guidance, lifestyle adjustments and follow-up consultations as needed. The aim is to move forward in a structured, supported way, with clarity at each stage rather than rushing into one-size-fits-all solutions.
Conclusion
SIBO can cause a wide range of symptoms, from bloating and abdominal discomfort to changes in bowel habits, fatigue and difficulty concentrating. Because these symptoms overlap with many other gut conditions, it is not always easy to understand what is driving them without proper assessment.
A structured, evidence-informed approach helps bring clarity. By combining appropriate testing, careful interpretation and personalised nutrition and lifestyle support, it becomes possible to move beyond guesswork and repeated trial-and-error strategies. At IBS Clinics, SIBO is approached as part of a wider picture, recognising the role of microbial balance, gut function and daily habits in shaping symptoms over time.
Rather than focusing on quick fixes, this approach supports people in understanding their symptoms, reducing their impact and building more sustainable digestive health going forward.
References
- Guts UK. Small Intestinal Bacterial Overgrowth (SIBO). https://gutscharity.org.uk/advice-and-information/conditions/small-intestinal-bacterial-overgrowth-sibo/
- Mayo Clinic. Small Intestinal Bacterial Overgrowth: Symptoms and Causes. https://www.mayoclinic.org/diseases-conditions/small-intestinal-bacterial-overgrowth/symptoms-causes/syc-20370168
- Institute for Functional Medicine. SIBO and Microbial Balance. https://www.ifm.org/articles/sibo-microbial-balance
Author – Tracey Randell
At IBS Clinics, Tracey Randell, a renowned Nutritional Therapist and one of the few IFM Certified Practitioners in the UK, extends her specialised knowledge and unique approach to managing and treating IBS and other gut-related conditions effectively.
Tracey’s profound understanding of Functional Medicine allows her to connect the dots for complex health conditions, identifying and addressing the root causes to curate personalised and comprehensive health plans for her patients. Her holistic approach focuses on resolving underlying imbalances and optimising gut health, enabling the body to correct other issues and attain overall well-being.
At IBS Clinics, we are dedicated to being your partner in navigating your gut-related health concerns, offering expert care and individualised treatment plans to alleviate your IBS symptoms and enhance your quality of life.
You can read more about Tracey on our About page here.
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