SIBO and IBS are often confused because the symptoms can look very similar: bloating, gas, abdominal pain, and a gut that alternates between diarrhea and constipation. But even though the two conditions are closely connected, they are not the same. They differ in what causes them, how they develop, and how they should be treated.
In this post, we’ll walk through what research says, how to tell them apart, and why many people who think they have IBS may actually have underlying SIBO.
What is IBS?
IBS (Irritable Bowel Syndrome) is a functional gut disorder. This means the gut doesn’t work as it should, even though no clear structural damage or measurable abnormalities can be found.
IBS is mainly characterized by:
In short, IBS is a condition where the gut behaves differently, but without a clearly identifiable physical cause.
What is SIBO?
SIBO (Small Intestinal Bacterial Overgrowth) occurs when bacteria that normally live in the large intestine start growing in the small intestine.
This leads to food being fermented in the wrong place, causing gas, bloating, and discomfort.
Unlike IBS, SIBO is:
-
Caused by a specific imbalance, bacterial overgrowth
-
Often linked to impaired digestion or gut motility
This makes SIBO a more defined condition, even if the symptoms overlap with IBS.
Why are SIBO and IBS often confused?
Several studies show that a large proportion of people with IBS-like symptoms actually have SIBO. That’s because both conditions can cause:
However, there are key differences that can help you understand what might be driving your symptoms.
Key differences in symptoms
While there is overlap, some patterns stand out:
More typical for SIBO:
-
Bloating shortly after eating (30–90 minutes)
-
Strong reactions to foods like onions, garlic, and beans
-
Nutrient deficiencies (e.g. B12, iron, fat-soluble vitamins)
-
Frequent burping or upper gas
-
Fatigue or brain fog after meals
More typical for IBS:
-
Symptoms that fluctuate with stress levels
-
Pain that improves after a bowel movement
-
Patterns linked to hormonal cycles (especially in women)
-
A more long-term, stable symptom pattern
In simple terms: SIBO is more closely tied to food intake, while IBS is more influenced by stress, the nervous system, and lifestyle.
Can you have both SIBO and IBS?
Yes, and it’s more common than many people think.
IBS can develop after an infection (so-called post-infectious IBS), which may also affect gut motility and increase the risk of SIBO. In these cases, both aspects often need to be addressed to see improvement.
How do you tell the difference?
The most reliable way to identify SIBO is a breath test. It measures hydrogen and methane gases in your breath and can indicate bacterial overgrowth in the small intestine.
IBS, on the other hand, is diagnosed by:
-
Ruling out other conditions
-
Evaluating symptom patterns
-
Using criteria such as the Rome IV guidelines
This means IBS is based more on clinical interpretation, while SIBO can be directly measured.
How are IBS and SIBO treated?
Because the root causes differ, the approach to treatment is also different.
For SIBO, focus is often on:
-
Supporting digestion
-
Improving gut motility
-
Addressing underlying causes
-
A probiotic supplement can sometimes be part of this process, especially when working toward restoring balance after overgrowth.
For IBS, focus is often on:
Treatment is therefore often more lifestyle-based and less biologically specific than in SIBO.
Summary
IBS is a functional disorder without a clear physical cause
SIBO is a measurable bacterial overgrowth
Symptoms can look very similar
But causes, development, and treatment differ
By understanding your symptoms, looking at digestion, diet, and gut motility and, if needed, testing you can often get closer to identifying what’s really behind your gut issues.
