SIBO: What You Need to Know

If you’ve been dealing with bloating, gas, food reactions, constipation, diarrhoea, or a gut that just doesn’t feel right, you may have come across the term SIBO—Small Intestinal Bacterial Overgrowth.

In many cases, people experiencing these symptoms have previously been given a diagnosis such as Irritable Bowel Syndrome.

While IBS describes symptoms, it doesn’t always explain what is driving them. In some cases, SIBO is a key underlying factor contributing to ongoing digestive dysfunction.

What SIBO Is & Why It Can Look Different in Everyone

SIBO occurs when there is an abnormal increase in the number of bacteria in the small intestine.

While the large intestine is home to trillions of bacteria, the small intestine normally contains far fewer. It is designed primarily for digestion and nutrient absorption, not fermentation.

When this balance is disrupted and bacteria from the large intestine overgrow into the small intestine, they begin fermenting food too early in the digestive process. This leads to gas production, bloating, pressure, and irritation in an area of the gut that is not designed to handle fermentation. This is why symptoms often appear soon after eating.

However, SIBO does not look the same for everyone. The type of gas produced influences symptom patterns:

• Hydrogen-dominant SIBO is more commonly associated with looser stools and faster gut transit.

• Methane-dominant SIBO (intestinal methanogen overgrowth) tends to slow gut motility, often leading to constipation, bloating, and a heavy or “stuck” feeling.

• Hydrogen sulfide SIBO is less commonly discussed but may present with variable bowel patterns, stronger-smelling gas, food sensitivities, fatigue, and more systemic symptoms.

These gas patterns are measured using a SIBO breath test, which assesses hydrogen and methane production during fermentation in the small intestine. While simple, results must always be interpreted alongside symptoms and clinical history.

Stool testing can also provide additional insight into overall gut health, including dysbiosis and digestive imbalance, although it does not diagnose SIBO directly.

Why SIBO Develops (The Bigger Digestive Picture)

SIBO usually develops when multiple digestive systems are not functioning optimally together over time.

• Low stomach acid reduces proper breakdown of food and allows bacteria to survive when they normally wouldn’t.

• Impaired gut motility, particularly dysfunction of the migrating motor complex (MMC), means the small intestine is not being properly cleared between meals. Allowing around four hours between meals can help support this process.

• Intestinal dysbiosis weakens the microbial balance of the gut, making overgrowth more likely.

• Bile flow plays an important antimicrobial role in the small intestine, helping regulate bacterial levels and support digestion. Fat digestion may also be affected, particularly if bile flow is impaired.

• The ileocecal valve can contribute when it is not functioning properly, disrupting flow between the small and large intestine.

• An underactive thyroid can slow overall digestive transit, increasing stagnation.

• Stress shifts the body into survival mode, reducing stomach acid, enzyme production, bile flow, and motility all at once

• Leaky gut (increased intestinal permeability), often driven by chronic inflammation or food sensitivities, can weaken the gut barrier and make small intestinal imbalance more likely.

• Previous gut infections, such as food poisoning, may disrupt gut motility or damage the gut lining, increasing the risk of SIBO developing later.

SIBO is also commonly associated with conditions such as Crohn’s disease, coeliac disease, and diabetes, which can impair normal digestive function and increase the likelihood of bacterial overgrowth.

How SIBO Affects Gut Health and the Wider Body

When SIBO persists, it begins to affect both day-to-day digestive function and overall wellbeing.

In the short term, along with the bloating, discomfort, and changes in how the body feels after eating, many people also experience fatigue, brain fog, or a general drop in energy.

This is partly due to the byproducts of bacterial fermentation in the small intestine, including compounds such as short-chain fatty acids (SCFAs), organic acids, amines, and ammonia. In the large intestine, these are produced through normal microbial activity, including the fermentation of fibre and the breakdown of proteins. Here they help support gut lining health, microbial balance, and a healthy pH environment. In the small intestine, however, they can become disruptive and contribute to the symptoms experienced in SIBO.

Over time, increased irritation in the gut lining can make the gut more reactive to foods and begin influencing immune activity.

If the imbalance persists, the gut also becomes less efficient at absorbing nutrients needed for energy, recovery, and resilience, such as iron, vitamin B12, magnesium, zinc, and fat-soluble vitamins A, D, E, and K.

Food Triggers: FODMAPs, Fructose & Histamine

Certain fermentable carbohydrates can significantly increase symptoms in SIBO.

Fructose is one example. It is found naturally in fruit, honey, and some vegetables, and is part of a broader group of fermentable carbohydrates known as FODMAPs. These carbohydrates are more easily fermented in the small intestine, leading to increased gas and bloating.

At the same time, histamine-containing foods can also become more difficult to tolerate.

Some bacteria produce histamine, and when the gut is inflamed, the body may struggle to break it down effectively. This can contribute to symptoms such as headaches, skin reactions, sinus issues, or digestive discomfort after foods like avocado, tomato, fermented foods, or leftovers.

This is not because these foods are harmful, but because the digestive environment has changed.

Treatment for SIBO & How Long It Takes

Supporting SIBO is not just about reducing bacterial overgrowth. It is about restoring the digestive environment so the imbalance does not continue to return.

Recovery is typically layered and individualised, and may include:

• Short-term dietary changes such as a Low FODMAP approach or a more specialised diet, such as the Specific Carbohydrate Diet (SCD), to reduce fermentation and ease symptoms

• Restoring digestive function, including stomach acid, bile flow, and gut motility (migrating motor complex)

• Prokinetic support to help maintain movement through the small intestine and reduce recurrence

• Digestive support such as enzymes or targeted nutrients where needed

• Stress and nervous system support, as digestion is closely linked to the body’s stress response

• In some cases, antimicrobials like oregano oil, berberine, and garlic extract or antibiotics (rifaximin, prescribed by a physician) are needed to help reduce bacterial overgrowth

• Gut-supportive nutrients such as glutamine and zinc, to help support gut repair and overall balance along with specific probiotics when needed

Because SIBO involves multiple systems, a more comprehensive approach that addresses these factors together is often most effective. Structured protocols, such as the GEMM approach, can help support digestion, microbial balance, gut repair, and motility within one framework.

SIBO is rarely resolved quickly.

Many people notice improvement within 8–12 weeks, while more complex or long-standing cases may take several months.

True resolution requires both reducing bacterial overgrowth and addressing the underlying dysfunction that allowed it to develop.

The Takeaway

SIBO is not just a bacterial imbalance—it reflects a breakdown in digestive function.

When you consider stomach acid, motility, bile flow, thyroid health, gut integrity, and stress together, the bigger picture becomes much clearer.

With the right support, the system can be brought back into balance.

If you’re unsure whether this could be contributing to your symptoms, it often helps to look at patterns rather than isolated symptoms.

Could This Be You?

Download the SIBO Symptom Checklist

If you want a simple way to see whether your symptoms align with SIBO, I’ve created a quick checklist you can work through.

Download The SIBO Check list

How I Can Help

If you’re dealing with ongoing gut symptoms, you don’t have to figure it out alone.

I take a personalised, root-cause approach to help you understand what is driving your symptoms and support your body properly.

Got a question? Book a Clarity Call

Let’s map out your next steps forward.