IBS vs. SIBO: symptoms, differences & how to tell them apart
Constantly bloated, gassy, or dealing with unpredictable bowel movements? Here's how IBS and SIBO differ, why their symptoms overlap, and what you should know before trying another gut health protocol.
You're bloated after meals. Your stomach feels uncomfortable by the end of the day. Some weeks you're constipated, other weeks you're running to the bathroom, and you can't seem to figure out which foods are causing the problem.
Maybe you've even been told you have IBS.
But then you start seeing people talk about something called SIBO, and suddenly you're wondering…
Wait, do I actually have IBS? Or could this be SIBO?
It's a question I hear often, especially from women who have spent years trying different diets, probiotics, and digestive supplements without getting the relief they're looking for.
Here's the thing: IBS and SIBO can look incredibly similar, but they're not interchangeable diagnoses.
And understanding the difference matters when deciding what to investigate and how to approach your symptoms.
1. What Is IBS?
IBS stands for irritable bowel syndrome, a common disorder of gut-brain interaction that affects how your digestive system functions.
People with IBS experience recurring abdominal pain associated with changes in bowel movements, such as constipation, diarrhea, or a combination of both.
There are several types of IBS:
IBS-C: Constipation-predominant IBS
IBS-D: Diarrhea-predominant IBS
IBS-M: Mixed IBS, involving both constipation and diarrhea
Bloating, gas, and abdominal discomfort are also common.
One important thing to understand is that IBS is a real medical condition. It isn't simply a diagnosis given when nothing else can be found, and it doesn't mean your symptoms are imaginary.
Factors such as altered gut motility, increased intestinal sensitivity, and gut-brain communication can all contribute to IBS symptoms.
And while stress can make symptoms worse, it isn't necessarily the underlying cause.
2. What Is SIBO?
SIBO stands for small intestinal bacterial overgrowth.
Normally, the small intestine contains fewer bacteria than the large intestine. With SIBO, an excessive number of bacteria are present in the small intestine, potentially interfering with normal digestive function.
These bacteria can ferment carbohydrates and produce gas, contributing to symptoms such as:
Bloating and abdominal distention
Excessive gas or belching
Abdominal discomfort
Diarrhea or changes in bowel habits
Feeling uncomfortably full after meals
In some cases, SIBO may also contribute to nutrient malabsorption.
There's also a related condition called intestinal methanogen overgrowth (IMO), which involves an overabundance of methane-producing microorganisms called archaea.
IMO is particularly relevant in people experiencing constipation, although constipation alone doesn't mean someone has methane overgrowth.
And here's where things get interesting.
3. Why Do IBS and SIBO Feel So Similar?
Because both conditions can involve changes in intestinal movement, gas production, and digestive sensitivity.
Someone with IBS might experience bloating because their intestines are particularly sensitive to normal amounts of gas or stretching.
Someone with SIBO might experience bloating because excess bacteria in the small intestine are fermenting carbohydrates.
And some people may have both conditions.
Research has found an association between IBS and positive SIBO breath tests, but the relationship is complicated. Breath tests have limitations, and not everyone with IBS has SIBO.
The important takeaway? Similar symptoms don't necessarily mean the same underlying problem.
That's why I don't recommend assuming every case of chronic bloating is caused by bacterial overgrowth.
4. How Do You Know Whether You Have IBS or SIBO?
This is where a thorough evaluation becomes important.
IBS is generally diagnosed based on a characteristic pattern of symptoms, particularly recurring abdominal pain associated with changes in bowel movements, along with an appropriate medical assessment.
Depending on your symptoms and history, your healthcare provider may recommend testing to evaluate for other conditions, such as celiac disease or inflammatory bowel disease.
SIBO, on the other hand, may be evaluated using a hydrogen and methane breath test.
These tests measure gases produced by microorganisms after you consume a specific sugar solution, typically glucose or lactulose.
However, breath testing isn't perfect. Results can be affected by intestinal transit time, test preparation, and the type of substrate used.
Testing is most useful when your symptoms and medical history make SIBO a reasonable possibility and the result would help guide treatment.
And despite what you may have seen online, a comprehensive stool test cannot diagnose SIBO, because stool testing primarily reflects microorganisms in the large intestine.
5. Why the Difference Matters for Your Gut Health
If you're struggling with ongoing bloating, gas, constipation, or diarrhea, it's tempting to try whatever gut health protocol you see recommended online.
Maybe that's a low-FODMAP diet, a probiotic, digestive enzymes, or an herbal antimicrobial supplement.
But these approaches aren't interchangeable, and what helps one person may not help another.
For example, someone with IBS may benefit from dietary adjustments, soluble fiber, gut-directed therapies, or treatments that address bowel habits and intestinal sensitivity.
Someone with confirmed SIBO may require medical treatment directed at bacterial overgrowth, along with evaluation of factors that could be contributing to it.
And someone with constipation related to pelvic floor dysfunction may need an entirely different approach.
This is why understanding what's contributing to your symptoms matters more than simply following another generic gut health protocol.
6. What If You've Been Diagnosed With IBS but Still Feel Terrible?
First, know that having IBS doesn't mean you should just accept feeling bloated and uncomfortable every day.
There are evidence-based strategies that can significantly improve symptoms and quality of life.
But if your symptoms aren't improving, it may be time to revisit your treatment plan and make sure other relevant conditions have been considered.
Some helpful questions include:
Are you having regular, complete bowel movements?
Have you been appropriately evaluated for celiac disease or other digestive conditions?
Are your symptoms primarily associated with constipation, diarrhea, or both?
Could medications, supplements, or dietary patterns be contributing?
Would additional testing or a gastroenterology referral be appropriate?
You don't necessarily need every gut health test available.
You need an individualized approach that considers your symptoms, health history, and the most appropriate next steps.
And if you're experiencing blood in your stool, unexplained weight loss, anemia, persistent vomiting, or severe abdominal pain, those symptoms deserve prompt medical evaluation rather than being attributed to IBS or SIBO.
Ready to Get to the Bottom of Your Digestive Symptoms?
If you've been dealing with chronic bloating, constipation, gas, or unpredictable digestion, I know how frustrating it can feel to keep trying different things without understanding what's actually going on.
As a functional nutritionist specializing in digestive health, I work with women who want a more personalized approach to improving their gut health.
Together, we look at your symptoms, nutrition, bowel habits, health history, and relevant testing to develop a plan that makes sense for your body, while coordinating with medical providers when appropriate.
Because you deserve more than another list of foods to avoid or supplements to try.
Explore My 1:1 Nutrition Programs
Or, if you're just getting started, download my FREE Bloat & Constipation Reset for simple ways to begin supporting your digestive health.
