IBS vs. SIBO: What's the Difference and Why Does It Matter?
You've changed your diet more times than you can count. You've cut out gluten, dairy, and everything in between. You've been told it's just IBS and that you need to manage your stress better. But the bloating keeps coming back, the bathroom trips are still unpredictable, and you're running out of patience.
Here's what you might not know: IBS and SIBO share so many of the same symptoms that even healthcare providers sometimes mix them up. But they're not the same condition, and that distinction matters more than you might think. As an Eugene digestive repair expert, I've seen countless clients spend months treating the wrong condition. Understanding which one you're dealing with is the difference between continuing to struggle and finally finding relief that actually lasts.
Let's break down what sets these conditions apart and why knowing the difference is so important for your healing journey.
The Bottom Line: IBS is a functional disorder where your gut isn't working properly, while SIBO is a bacterial overgrowth in your small intestine. They feel similar but need different treatments. Knowing which one you're dealing with changes everything.
What Is IBS?
IBS (Irritable Bowel Syndrome) affects about 10-15% of people worldwide. It's what we call a functional disorder, meaning your digestive system isn't functioning the way it should, even though there's no visible damage to your gut tissue.
The hallmark symptoms include abdominal pain, bloating, and changes in bowel habits like diarrhea, constipation, or both. For many people I work with here in Eugene, stress and certain foods trigger flare-ups that can derail your entire day.
IBS comes in three types:
IBS-D (diarrhea-predominant)
IBS-C (constipation-predominant)
IBS-M (mixed symptoms)
Here's what makes IBS so frustrating: triggers vary dramatically from person to person. What sets off your symptoms might not bother someone else at all. Stress, hormonal changes, specific foods, even the rainy Oregon winter can all play a role. This is exactly why cookie-cutter treatment plans rarely work for long.
What Is SIBO?
Now let's talk about what makes SIBO different.
SIBO (Small Intestinal Bacterial Overgrowth) happens when too much bacteria accumulates in your small intestine, a place that's supposed to have relatively few bacteria compared to your large intestine. When this delicate balance gets disrupted, you end up with many of the same uncomfortable symptoms as IBS, but the root cause is completely different.
The most telling SIBO symptoms include:
Severe bloating that worsens throughout the day
Excessive gas
Abdominal pain
Diarrhea
Nutrient deficiencies (leading to fatigue or unexplained weight loss)
Here's what many people don't realize: those excess bacteria interfere with your body's ability to absorb vitamins and minerals from food. This means you might feel chronically fatigued or notice unexplained weight loss, even when you're eating well.
A 2023 study found that about 36% of people diagnosed with IBS actually have SIBO. That's more than one in three. This overlap is why so many people spend months or even years trying IBS treatments that don't work. They're treating the wrong condition.
How the Symptoms Overlap (and Where They Differ)
Both conditions share these common symptoms:
Abdominal pain and cramping
Bloating
Diarrhea
Constipation
On the surface, they can feel identical, which is exactly why misdiagnosis happens so often. But there are subtle differences worth paying attention to.
With SIBO, bloating tends to be more severe and progressive throughout the day. Many people describe feeling like they look pregnant by evening. You might also notice oily stools, unexplained fatigue that doesn't improve with rest, or vitamin deficiencies showing up in blood work.
IBS symptoms, on the other hand, are often more tied to stress and specific food triggers. You might notice that your symptoms flare after a tough week at work or when you eat certain foods. The unpredictability itself becomes part of the problem, making it hard to plan your day or enjoy activities around Eugene, from Saturday Market to dinner at your favorite restaurant.
One of my clients described it perfectly: "The bloating was unbearable until we identified it as SIBO, not IBS." Once she got the right diagnosis, everything changed.
Why These Conditions Get Confused
Understanding what causes each condition helps explain why they're so often mistaken for one another.
IBS develops from a combination of factors:
Disrupted gut-brain communication (where stress directly impacts your digestive system)
Food intolerances
Hormonal fluctuations
Gut motility issues
It's complex and highly individualized, which is why treatment needs to be personalized too.
SIBO typically develops when something disrupts your gut's natural defenses:
Slowed digestive motility (like a traffic jam in your intestines)
Anatomical changes in your gut (such as strictures or diverticula)
Underlying conditions like diabetes or celiac disease
Post-infection issues (some people develop SIBO after food poisoning)
Antibiotic use that disrupts bacterial balance
Here's what makes this tricky: up to 15% of people with chronic diarrhea actually have SIBO, not IBS. And about 50% of people with celiac disease develop SIBO. These aren't rare occurrences. The conditions frequently coexist or get mistaken for one another.
How to Get the Right Diagnosis
Getting tested is straightforward once you know what to look for.
For IBS, doctors use what's called the Rome IV criteria, which is based on your symptom history. You'll need to have recurrent abdominal pain at least once a week for three months, along with changes in how often you go to the bathroom or what your stool looks like.
For SIBO, the gold standard is a breath test. You'll drink a solution containing lactulose or glucose, then breathe into a collection device at timed intervals. If you have SIBO, the excess bacteria will ferment the sugar and produce measurable levels of hydrogen or methane gas. It's non-invasive and gives us clear data about what's happening in your gut.
In my practice here in Eugene, I use SIBO breath testing as part of a comprehensive approach to understanding digestive health. Functional lab testing can finally give you the clarity you've been looking for by revealing exactly what's happening in your gut.
The challenge is that many people never get tested for SIBO. They're diagnosed with IBS based on symptoms alone and sent home with generic advice that doesn't address the underlying problem.
Why the Right Diagnosis Changes Everything
Let's be honest: if you're treating IBS when you actually have SIBO, you're not going to get better. You might see temporary improvements, but the symptoms will keep coming back.
SIBO requires targeted treatment, often starting with antibiotics like rifaximin or herbal antimicrobials, followed by specific dietary protocols to prevent recurrence. About 45% of people experience SIBO recurrence within three months if the root cause isn't addressed, which is why a comprehensive approach matters.
IBS treatment looks different. It focuses on dietary modifications like the Low FODMAP diet, stress management techniques, and sometimes medications to manage specific symptoms. These approaches can be incredibly effective for true IBS, but they won't eliminate bacterial overgrowth.
When you get the right diagnosis, treatment becomes targeted instead of guesswork. You stop wasting time and money on solutions that were never going to work. And most importantly, you finally start feeling better.
In my practice, I take a holistic approach that considers your complete health picture. We don't just look at symptoms; we dig into root causes, run appropriate testing when needed, and create personalized treatment plans that address what's actually happening in your gut.
Ready to Get Real Answers About Your Gut Health?
If you're tired of guessing, trying random diets, and feeling frustrated by symptoms that won't go away, I'd love to help you find a different path forward.
You deserve to know exactly what's causing your digestive issues. Whether it's IBS, SIBO, or something else entirely, getting the right diagnosis is the first step toward feeling like yourself again.
Here in Eugene, I specialize in getting to the root of digestive problems with personalized, sustainable solutions. My 6-month digestive repair program combines functional testing, targeted treatment, and ongoing support to help you reclaim your energy and confidence.
Book your free discovery call today, and let's talk about what you're experiencing. Together, we'll create a path forward that actually works for your body and your life.
Frequently Asked Questions
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Yes, absolutely. Studies show that 60-80% of people with IBS actually test positive for SIBO. This is why comprehensive testing is so important. When both conditions are present, treatment needs to address the bacterial overgrowth first, then focus on managing IBS symptoms and preventing recurrence.
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Initial herbal antimicrobial treatment typically lasts 3-6 months. However, SIBO has a high recurrence rate (about 45% within three months) if underlying causes aren't addressed. A comprehensive approach that includes dietary changes, prokinetic support, and addressing root causes usually takes 6 months for lasting results.
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The Low FODMAP diet can help reduce symptoms during and after SIBO treatment, but it won't eliminate the bacterial overgrowth on its own. SIBO requires targeted antimicrobial treatment. That said, a modified Low FODMAP approach is often part of a comprehensive SIBO treatment plan.
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Several functional medicine practitioners and gastroenterologists in the Eugene-Springfield area offer SIBO testing. In my practice, I use SIBO breath testing as part of a comprehensive digestive health assessment. During your discovery call, we can talk about whether testing makes sense for your situation.
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There are two main types: lactulose and glucose breath tests. Both measure hydrogen and methane gases produced by bacteria. The lactulose test takes longer (about 3 hours) but can detect SIBO throughout the small intestine. The glucose test is shorter (about 2 hours) but may miss overgrowth in the lower small intestine. I often use fructose (a 3 hour test), as it catches SIBO at a higher rate than the others. We'll choose the best option based on your specific symptoms.
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Stress doesn't directly cause SIBO, but it can be a contributing factor. Chronic stress affects gut motility (the movement of food through your digestive system), and slowed motility is one of the main risk factors for SIBO development. Stress also impacts your immune system and gut barrier function, which can create conditions where bacterial overgrowth is more likely to occur.
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SIBO bloating typically gets progressively worse throughout the day and is often described as severe distension (looking visibly pregnant). IBS bloating tends to be more variable and closely tied to specific food triggers or stress. The only way to know for sure is through proper testing, particularly a SIBO breath test.