SIBO: the overlooked cause of bloating

When bloating won't behave like a normal food reaction, the answer might be bacteria in the wrong place.

July 2, 2026

Some bloating behaves the way you'd expect: a specific food, a clear reaction. But some bloating is different - relentless, there most days, often worsening through the day, and stubbornly resistant to whatever you cut out. You've probably been told it's "just IBS."

There's a specific, common, and frequently missed explanation for that kind of bloating - and it isn't a food at all. It's bacteria growing in the wrong part of your gut. It's called SIBO.

What SIBO actually is

Your gut bacteria are supposed to live mostly in your colon - the large intestine - which is densely populated by design. Your small intestine, by contrast, is meant to stay relatively sparse, with far fewer bacteria.

SIBO - small intestinal bacterial overgrowth - is exactly what the name says: an excess of bacteria, often colon-type bacteria, colonising the small intestine where they don't belong.¹

That misplacement is the whole problem. The right bacteria, in the wrong place, do the wrong things.

Why that causes bloating and gas

When bacteria ferment carbohydrates, they produce gas - hydrogen, methane, carbon dioxide. In the colon, that's normal and expected. In the small intestine, it means fermentation is happening too high up and too early - so gas builds where it shouldn't, stretching and distending the small bowel.

The result: bloating is the single most common SIBO symptom, reported by most patients, along with excessive gas.² It can also bring diarrhoea, constipation, nausea and abdominal pain - and, when overgrowth is significant, the bacteria can interfere with nutrient absorption, which is why fatigue, weight loss and vitamin deficiencies can follow.²

The real root: a motility problem

Here's the genuinely insightful part - the bit that explains why SIBO happens.

Your small intestine has several defences that keep it relatively bacteria-free: stomach acid, bile, digestive enzymes, the valve between the small and large intestine, and - most importantly - movement. Between meals, the small intestine runs a series of cleansing waves, the "migrating motor complex," that sweep leftover food and bacteria onward toward the colon. It's a housekeeping system.¹

SIBO tends to take hold when that housekeeping fails - most often when motility slows down. If things don't move through the small intestine briskly enough, bacteria aren't swept out; they settle, and they multiply. Surgery, certain conditions, and motility disorders can all slow that transit and create the conditions for overgrowth.²

So at root, SIBO is often not a "bad bacteria" problem so much as a plumbing problem - a gut that isn't clearing itself.

Why it overlaps so heavily with IBS

This is why SIBO gets missed. It hides inside an IBS diagnosis.

IBS, intestinal motility disorders and chronic pancreatitis together account for the large majority of SIBO cases.¹ And the overlap runs the other way too: small-intestinal microbial disturbance has been implicated in the symptoms of functional gut disorders like IBS.³ The two are deeply tangled.

The practical takeaway: if you've been labelled "IBS" and your dominant, defining symptom is relentless bloating and gas, SIBO is a possibility genuinely worth being aware of - because it has a specific explanation and a different angle of attack than "IBS" alone suggests.

How it's identified

SIBO is typically investigated with a breath test - measuring the hydrogen and methane that overgrown bacteria produce after a test dose of sugar - while the formal gold standard is a culture taken directly from the small intestine.¹ It isn't something you can confirm from symptoms alone. But the symptom pattern - and how it tracks with food - is exactly what tells you whether it's worth pursuing.

The food connection

SIBO isn't caused by diet - it's a bacterial and motility issue. But food powerfully shapes how it feels.

Because the symptoms are driven by bacterial fermentation of carbohydrates, they track closely with fermentable carbs - the FODMAPs.⁴ That's why lowering fermentable carbohydrate tends to ease SIBO-type bloating: you're giving the misplaced bacteria less to ferment. It also means that even though SIBO is a "bacteria" problem, tracking your food still reveals a great deal - the shape, the timing and the carbohydrate-dependence of your bloating.

My bloating didn't behave like a food allergy - it was just always there, worse by evening. Tracking showed it climbed with fermentable carbs across the whole day, not one meal. That was the clue that finally pointed somewhere specific.

Finding your pattern

Even with a bacterial cause, your own data is what makes the picture clear. Worth tracking:

The shape of the bloating - does it build through the day, regardless of any single meal?
Carbohydrate load - do fermentable carbs (FODMAPs) consistently make it worse?
The other symptoms - gas, bowel changes, fatigue - and how they move together.
Whether it tracks specific foods at all - or whether it's there almost regardless.

That last contrast is the useful one: bloating that follows specific foods points toward a food trigger; bloating that's near-constant and carbohydrate-driven points toward something like SIBO. Either way, you end up with real evidence instead of a guess - and a clear sense of whether things are improving over time.

Where Triggerbites fits in

Triggerbites is built to make the shape of a symptom visible.

You log meals and bloating in plain language, and it extracts the ingredients, tags the fermentable carbohydrates, and correlates them with your symptoms across the day and across time windows. It can show you whether your bloating is one-meal-and-done, or a slow all-day climb with carbohydrate load - the distinction that separates a simple food trigger from a SIBO-type pattern.

Log like you're texting - plain language, not database searches

Automatic ingredient breakdown - we parse your entries into the basic components so you don't have to

Built-in chemical tagging - FODMAP, histamine, salicylates, oxalates ++ more compounds flagged automatically

Multi-window pattern recognition - correlations across same-day, next-day, and multi-day windows

Reports you can share - something to take to a doctor or dietitian

It takes seconds a day, and the trend it builds is a clear, concrete thing to share with a doctor - especially useful when the question is whether SIBO is worth investigating.

For the wider picture of bloating, see why am I bloated after everything I eat?

Live, love, log. 🧡

References

1
StatPearls, NCBI Bookshelf "Small Intestinal Bacterial Overgrowth"NCBI Bookshelf
2
Mayo Clinic "Small Intestinal Bacterial Overgrowth (SIBO): Symptoms & causes"Mayo Clinic
3
U.S. National Library of Medicine (PMC) "Small intestinal microbial dysbiosis underlies symptoms associated with functional gastrointestinal disorders", 2019PMC
4
Advances in Therapy "Bloating and Abdominal Distension: Clinical Approach and Management", 2019Springer